A more thorough explanation:

The equitable-restraint doctrine is a legal principle that refers to a federal court's decision not to interfere with an ongoing state criminal proceeding or civil proceeding used to enforce criminal law, unless the prosecution has been brought in bad faith or merely as harassment. This principle is also known as Younger abstention.

For example, if a person is facing criminal charges in a state court, a federal court may choose not to intervene in the case unless there is evidence that the prosecution is being used to harass or discriminate against the defendant. Similarly, if a state court is using a civil proceeding to enforce criminal law, such as abating an obscene nuisance, a federal court may choose not to interfere.

The equitable-restraint doctrine is based on the idea that state courts should have the authority to enforce their own laws and that federal courts should only intervene in exceptional circumstances. This principle helps to maintain the balance of power between state and federal governments and ensures that each court system can carry out its own responsibilities without unnecessary interference.