In modern pop culture, "bet" is a slang word used as a quick form of acknowledgement, usually in place of "OK." Players initially used the word as a way to acknowledge Harbaugh's three-game suspension due to Michigan's illicit sign-stealing scandal and to let people know they would be locked-in on proving their ...
The term bet can be used in a few different ways, but generally means "agreed" or "okay". For example, if someone says "Wanna grab lunch later?" and the other person responds "Bet", it means they agree to the plan.