The US doesn't have public interest standing as some other countries do. However, organizations can represent their members, and in some instances, someone can represent the rights of others if they have been injured -- this is often allowed if the other injured parties would not be able to seek redress themselves.
For example, an 18 y/o denied an FOID for lack of a parents signature might have their case languish for 3 years such that they turn 21 and could get an FOID without a parent's signature. The court, recognizing that the next 18 y/o would also have their case languish for years, may allow the case to continue even if the standing question becomes murky due to the plaintiff turning 21. Horsley v. Trame was nearly in this situation.
Edited by Silhouette, 15 March 2019 - 02:32 PM.