Hey there… Welcome to the forum.
A Cleanser is a hero who removes negative statuses from him/herself, to him/herself + nearby allies, or the entire party (the game has evolved quite a bit so there is that distinction amongst the many heroes it has, there are also status ailments that “cannot” be cleansed)). What you were referring to is a Dispeller, as someone who removes a positive buffs from the intended target(s) (similar to the Cleanse, there are also buffs that cannot be dispelled).
As for your question on the lingos and jargons people use, you may find this post interesting:
Some of the information in the compilation may be a bit outdated, but are still mostly accurate. There are just too many new heroes, new mechanics, new abilities, way too fast.