A lawsuit that asks a court to answer a question. In a patent context, the court is asked whether or not a certain activity constitutes patent infringement. The action is commenced by an accused infringer in its local federal court so that the accuser (the patent owner) must travel to the infringer’s location to try the lawsuit. Declaratory judgment lawsuits are frequently filed in response to cease and desist letter.

https://smithhopen.com/glossary/cease-and-desist-letter/
Drafting Cease and Desist Letters