Tank
A tank is a Pokemon with attacking and defending abilities.
Sweeper
A sweeper is a role that is the name exactly. It sweeps the Pokemon out of the way, ususally with just a few hits.
Wall
A Pokemon with amazing defensive abilities that can stall and help set up.
Physical Sweeper
A sweeper with physical moves and high attack.
Special Sweeper
A sweeper with special moves and high special attack.
Mixed Sweeper
A Pokemon with with good offensive stats and both physical and special moves.
Annoyer
An annoyer basically annoys other Pokemon ie. Substitute with Leech Seed.
Baton Passer
A baton passer is a Pokemon that uses many stat raising moves and uses Baton Pass to switch to a different Pokemon with those boosts still intact.
Cleric
A cleric is a healer ie. Blissey with Wish.
Drainer
Just guessing here, but a drainer is a Pokemon that uses moves to drain the other Pokemon's HP to use for itself. Moves would include things like Drain Punch, Giga Drain, Leech Seed, etc.
Spiker
A Pokemon that sets up moves like spikes and toxic spikes.
