On June 17, 2011, Immigration and Customs Enforcement (ICE) Director John Morton issued a memorandum directing ICE staff to consider declining to put people in removal proceedings, terminating proceedings, or delaying removals in cases where people have longstanding ties to the community, U.S.-citizen family members, or other characteristics.

https://www.ice.gov/doclib/secure-communities/pdf/prosecutorial-discretion-memo.pdf

“Prosecutorial discretion” is the authority of an agency or officer to decide what charges to bring and how to pursue each case. A law-enforcement officer who declines to pursue a case against a person has favorably exercised prosecutorial discretion. The authority to exercise discretion in deciding when to prosecute and when not to prosecute based on a priority system has long been recognized as a critical part of U.S. law. The concept of prosecutorial discretion applies in civil, administrative, and criminal contexts. The Supreme Court has made it clear that “an agency’s decision not to prosecute or enforce, whether through civil or criminal process, is a decision generally committed to an agency’s absolute discretion.” Heckler v. Chaney 470 U.S. 821, 831 (1985).

Prosecutorial discretion may be exercised at any stage of an immigration case. Specifically, prosecutorial discretion may be exercised when deciding whether to: issue a detainer; initiate removal proceedings; focus enforcement resources on particular violations or conduct; stop, question, or arrest a particular person; detain or release someone on bond, supervision, or personal recognizance; settle or dismiss a removal case; stay a final order of removal; pursue an appeal; and/or execute a removal order.

Prosecutorial discretion exists whenever a government official is empowered to decide whether to pursue charges against someone. Consequently, prosecutorial discretion is inherent in our system of laws, regardless of the substantive issue. In the immigration context, research conducted by Shoba Sivraprasad Wadhia shows that immigration agencies and officials have a long and rich history of using prosecutorial discretion to resolve cases involving significant equities, policy calls, or practical resource issues. In 2000, then-INS Commissioner Doris Meissner issued guidance clearly articulating the role of prosecutorial discretion in immigration enforcement. That guidance remains in operation and has served as the touchstone for a series of other DHS memos on exercising discretion. The Morton Memo on prosecutorial discretion is the most recent of at least thirteen such memos.

In short, prosecutorial discretion is about exercising good judgment.