What does "cop a plea" mean?

Plead guilty or confess to a crime in exchange for a lighter sentence; also, plead guilty to a lesser charge in exchange for not being tried for a more serious charge. For example, Arnold decided he was better off copping a plea than facing a jury. [Colloquial; 1920s]

Plead for mercy; make excuses. For example, He copped a plea about not knowing his way around. [Slang; c. 1940]