It could be oversight, under-learning or such but on and off I remember that I never learned what to call the game-changer "-s" that comes in to distinguish plurals from singulars. "Plural -s" is all that I learned and use.
Of as much significance is the "-s" that the apostrophe brings with it in the forms of words variously described as possessive, attributive, genitive or ownership. I've been referring to it as the respective "-s," i.e., "possessive -s," etc.
Would have saved a lot of breath if these two applications of the "s" had a name in grammar. Hopefully at least one of them does.