A more thorough explanation:

Definition: Giser (jI-sər), vb.[Law French] Hist. (Of an action) to lie; to be capable of being brought as a suit in court.

This means that giser refers to the ability of a legal action to be brought to court. It is often used in phrases such as "ou assise ne gist point" (when an assise does not lie), "le action bien gist" (the action well lies), "gist en le bouche" (it lies in the mouth), and "cest action gist" (this action lies).

For example, if someone wants to sue another person for breach of contract, they would need to determine if the action "lies" or gists in court. If it does, they can proceed with the lawsuit. If it does not, they cannot bring the case to court.