Anyone know what these represent?
It's really hard, actually pretty near impossible, to answer this without knowing the context you're seeing these in.
Im guessing your seeing these in relation to physics, motion?
All of those 3 mean the same thing. Units for velocity, or speed.
m is metres, s is seconds.
Meters per second is m/s. since 1/s is equal to s-1, we write it like the ways you stated.
Do you mean m s-1?
If so, that's the same as m/s or "meters per second" as Gib Z said.
Separate names with a comma.