They the same thing with possible procedural differences (what they get called depending on the type of case) in some places https://en.wikipedia.org/wiki/Plain

They the same thing with possible procedural differences (what they get called depending on the type of case) in some places https://en.wikipedia.org/wiki/Plaintiff https://en.wikipedia.org/wiki/Plaintiff Legally speaking they are different, but to the layperson they mean the same thing (both are the ones on the opposite side of the defendant).