MH/s, GH/s, MHz, GHz: what does it mean?

[epixoip]

Yes, MH/s is "megahashes per second", as in 1000000s of hashes per second.

H/s == Hashes per second
KH/s == Kilohashes per second (Thousands of hashes per second)
MH/s == Megahashes per second (Millions of hashes per second)
GH/s == Gigahashes per second (Billions of hashes per second)
TH/s == Terahashes per second (Trillions of hashes per second)
PH/s == Petahashes per second (Quadrillions of hashes per second)

So on and so forth.