Originally Posted by
Dr1Gonzo
My terminology is all messed up then. On a MTB, what do you call the 6 or 7 rings around the back freewheel/cassette - not cogs?
You just answered your own question, as a whole unit they are either a freewheel or a cassette. Each individual toothed wheel is called a sprocket.
When you are talking about non-geared bikes you talk of freewheels, which are lone sprockets that can coast because they have a freewheel type clutch mechanism built in, or you talk of cogs, which are lone sprockets that can't coast.
When you talk about (dérailleur) geared bikes, then a freewheel is the same but with more sprockets attached. Cassettes are multiple sprockets with no clutch, because it's inside the hub instead.