A Bruiser is a tank and an attack damage mix. bruisers generally also have pretty strong lane sustain that allow
them to farm. They're steady and reliable DPS for your team, not high or accurate enough to be a classic carry but enough of a threat to warrant focusing.
They can also dish out TONS OF DAMAGE (As Phreak would say), but not enough to count as a true Carry.
A couple of Bruiser Champions are:
Garen
Darius
Irelia
Renekton