What is Bet ?
Bet is (noun) a sum of money which is risked by trying to say which horse will come first in a race or which side will win a competition, etc. He placed a bet on his friend’s horse but lost his bet when the horse came last. I’ve got a bet on England to win the next World Cup. it is a safe bet it is very likely to happen It’s a safe bet that if we decide to go camping it will rain. ((verb)) 1. to risk money by saying which horse you think will come first in a race or which team will win, etc. He bet me £10 the Prime Minister would lose the election. 2. to be sure of something I bet you she’s going to be late. you bet! of course (informal.) Do you want to go to the pub? You bet!
source: Easier English, Student Dictionary Upper Intermediate Level