Note: this Glossary is not intended to describe the below terms for all purposes, but just as they are likely to appear in the Litigation Tracker.  Definitions for additional legal terms can be found at the U.S. Court’s Glossary of Legal Terms.

Administrative Procedure Act (APA)

The United States federal statute that governs the actions of administrative agencies (e.g., the Department of Homeland Security, the Department of State, etc.), mostly by requiring that they go through particular procedures when making sufficiently important decisions.

Border Wall

One or more physical barriers at the United States’ international border, particularly its southern border with Mexico. Extending existing border walls was a central theme of President Trump’s administration, notwithstanding the significant costs (of all kind) and diminishing returns. Once inaugurated, President Biden ordered a cessation of additional border wall construction (although some has seemingly continued); litigation ensued.


the document that typically begins a civil lawsuit, in which the plaintiff (the party bringing suit) sets out the claims against the defendant and identifies the action requested of the court (typically, that the court order specified relief, like an injunction of the challenged policy).  Complaints are frequently amended over the course of litigation (for example, to add or drop claims or parties).


refers to COVID-19, the infectious disease caused by the SARS-CoV-2 coronavirus. President Trump and now President Biden have both used the COVID-19 pandemic to justify severe restrictions on immigration, particularly on asylum seekers fleeing persecution and violence in their home countries.


appealing when the other party has also appealed. Whoever notices the appeal second is referred to as the cross-appeal.


Deferred Action for Childhood Arrivals (“DACA”) is a policy of the U.S. Department of Homeland Security under which certain undocumented immigrants brought to the United States as children can apply, on a case-by-case basis, for a reprieve from deportation for a temporary period (currently, for two years) and, during that period, employment authorization.  If the applicant meets eligibility and other criteria, DHS may “defer” (i.e., postpone) taking “action” to deport that individual as a matter of prosecutorial discretion (hence the name “deferred action”). DACA is renewable, but it does not grant legal status or a path to citizenship.

DACA was created in 2012 by then-DHS Secretary Janet Napolitano.  The Trump Administration repeatedly tried to end DACA, but those efforts were blocked by various federal courts (as ultimately affirmed by the Supreme Court in 2020) on procedural grounds.  In July 2021, a federal judge in Texas ruled that DACA is unlawful and enjoined (blocked) DHS from granting any new DACA applications; renewals may still be granted.  That decision is currently on appeal.


the action of removing a foreigner from a country; in U.S. immigration law, also referred to as “removal.”  In the United States, noncitizens are entitled to some process before being deported (e.g., an opportunity to be heard on why they should not be deported), although that process is frequently quite scant.


a pretrial process in civil litigation through which each side can obtain factual information relevant to the lawsuit from the other side and from third parties. Not every case involves discovery, but in those that do, litigants most commonly use the discovery process to obtain copies of documents or a witness’s testimony (the latter via depositions).  


The act of legally prohibiting or mandating a party to a case to do something specific, through issuance of an injunction.  See also Injunction, infra.


the action of summarily removing a foreigner from the United States with virtually no process at all (e.g., with no opportunity to be heard on why they should not be removed, including on asylum grounds, in contrast to deportations), under the auspices of the public health law.  See also Title 42, infra


Immigration and Customs Enforcement (“ICE”) is the federal law enforcement agency principally tasked with enforcing U.S. immigration law through the arrest, detention, and deportation (“removal”) of noncitizens.  ICE is housed within the U.S. Department of Homeland Security.  Either directly or through contracts, ICE maintains detention facilities across the country where tens of thousands of noncitizens (on any given day) are held while they await resolution of their immigration cases and/or deportation.  ICE also conducts actual deportations of individual noncitizens, including through its air transportation arm, “ICE Air.”


a court order that prohibits or requires a party to the case to do something specific; for example, an injunction may prohibit a federal agency responsible for enforcing a challenged policy from doing so.

A preliminary injunction is issued relatively early in a case, typically upon a showing that the party bringing suit is being irreparably harmed by the challenged action, is likely to prevail in proving that the challenged action is unlawful, and that it would be equitable to issue the requested injunction.  A preliminary injunction only lasts until the court can consider the full merits of the lawsuit, to determine whether a permanent injunction is appropriate.

Judge Shopping

the practice, usually by the plaintiff (i.e., the party who files a lawsuit), to use procedural rules to steer the case to one or more specific judges the plaintiff believes will be more favorable to the case. Red states challenging immigrant inclusive policies of the Biden Administration typically judge shop by filing their cases where they are likely to have their cases decided by specific, usually Trump-appointed judges.  See also “Can plaintiffs pick their judge?” in our FAQs

Mandatory Detention

Mandatory detention is the practice of imprisoning an individual under specified circumstances, without regard to whether doing so is necessary or appropriate in the individual case.  U.S. immigration law subjects various categories of noncitizens to mandatory detention, including certain asylum seekers; certain noncitizens subject to a final order of removal; and noncitizens who are deportable because of certain criminal activity–a category that includes even long-time green card holders convicted of relatively minor drug or theft offenses.  Most immigrants detained in the United States are mandatorily detained, more than 200,000 immigrants are subjected to mandatory detention every year (pre-pandemic), and many are detained for prolonged periods. 

Notwithstanding the outsized role mandatory detention already plays in the U.S. immigration system–and the significant costs it imposes on detained immigrants, their family, and U.S. taxpayers–a common theme in lawsuits brought against the Biden Administration is that the particular challenged policy conflicts with one or more mandatory detention provisions, by not enforcing it how those bringing suit would prefer.


The situation when a controversy no longer exists, which typically means a federal court can no longer decide the matter, as it would have no practical significance.  In civil litigation, a motion, an appeal, or an entire case can become moot, typically when the relief requested (in the motion, appeal, or case) has been obtained or could no longer be ordered by a court.

Motion to dismiss

 a request, usually by the defendant to a lawsuit, that the court terminate all or a portion of a lawsuit upon the court’s conclusion that it should not be permitted to proceed.  


The situation when a controversy no longer exists, which typically means a federal court can no longer decide the matter, as it would have no practical significance. In civil litigation, a motion, an appeal, or an entire case can become moot, typically when the relief requested (in the motion, appeal, or case) has been obtained or could no longer be ordered by a court.

MPP/RMX (Remain in Mexico)

under the "Remain in Mexico" program (RMX), also referred to as the "Migrant Protection Protocols" (MPP), noncitizens who arrive at the southern border and ask for asylum are given notices to appear at a future date in a U.S. immigration court at the border, and then returned to Mexico to wait for however long it takes for the U.S. government to process their applications for humanitarian protection.  The program was created by President Trump in late 2018.  On the campaign trail, President Biden promised to end RMX, and attempted to do so soon after he was inaugurated; litigation ensued.


A court’s written explanation for its decision in a particular case.


in the immigration context, “parole” is official permission, granted at the discretion of the Department of Homeland Security, for a noncitizen to remain in the United States for a temporary period.  Parole can be granted to noncitizens inside or outside the United States, and in a range of circumstances.  Parolees are not considered “admitted” to the United States under immigration law, and parole does not entitle the beneficiary to permanent status or a path to citizenship.  By statute, parole can be granted “only on a case-by-case basis for urgent humanitarian reasons or significant public benefit.”

Prosecutorial Discretion

the traditional and customary authority of any law enforcement agency to decide where to focus its resources and whether or how to enforce (or not) the law against individuals. 


a temporary pause to a judicial proceeding or a part thereof.  In civil litigation, “stay” is most commonly used in reference to a court order (e.g., “stay of the injunction pending appeal”), a motion (“briefing on the appeal is stayed”), or to a case in its entirety (“the case was stayed”).

Take Care Clause

Section 3 of Article II of the U.S. Constitution states that, among other things, the President “shall take Care that the Laws be faithfully executed.” 

Temporary restraining order

akin to a preliminary injunction, a “TRO” is a judge's short-term order forbidding certain actions until a full hearing can be conducted.  Unlike preliminary injunctions, TROs are limited by rule to 14 days (although they can be extended in certain circumstances).

Title 42


The situation when a controversy no longer exists, which typically means a federal court can no longer decide the matter, as it would have no practical significance.  In civil litigation, a motion, an appeal, or an entire case can become moot, typically when the relief requested (in the motion, appeal, or case) has been obtained or could no longer be ordered by a court.

The U.S. Code (the collection of statutes passed by Congress) is divided into more than 50 subjects, called “Titles”; Title 42 contains the public health statutes, including a previously obscure provision (Section 265) authorizing the Center for Disease Control and Prevention (CDC) to prohibit “the introduction” into the United States of “persons and property” if doing so is “necessary” to avert “serious danger” of “introduc[ing]” a “communicable disease” into the United States.  In March 2020, and ostensibly to prevent the spread of COVID-19, the Trump CDC issued an order under this provision prohibiting the “introduction” of certain individuals into the United States from Mexico or Canada–in particular, those who would normally be detained by DHS after arriving at the border, such as asylum seekers.  On the same day, DHS began “expelling” such individuals arriving at the U.S.-Mexico border back to Mexico, without giving them the opportunity to apply for asylum or other forms of humanitarian protection–notwithstanding that Title 8 of  U.S. Code (the immigration law) protects the right to apply for asylum.  The CDC under President Biden largely kept the Title 42 expulsion orders in place until April 2022, when it announced that the final Title 42 expulsion order would sunset on May 23, 2022.


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