Hackmons is a tier where Pokemon can have maxed out EVs, any ability, and any combination of moves. It is noticeably different than standard because there's stuff like Sturdy Shedinja, Contrary Deoxys-S, Huge Power Slaking, etc. Basically, anything goes.
Balanced Hackmons has developed from that. It's the same as Hackmons except OHKO moves, Huge Power, and Pure Power are banned (they were deemed unbalanced, hence the name).