Crowd Control (commonly shortened to CC) is a blanket term used in MMORPGsand MOBAs which are movement-impairing abilities or items. Slows, stuns, knockups, other displacement abilities - everything that prevents you from moving normally. The more of those abilities a hero has, the more CC he offers. CC Heroes are mostly Tanks, Fighters, Mages and Supports.
There are currently 21Heroes with the Crowd Control Specialty.