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. Bet" can also be used as a response to confirm that a statement is true.
When Singapore passed the Remote Gambling Act, many major foreign bookmakers stopped operating in the country to comply with the new laws. Bet365 is among the sites that is no longer available to users in Singapore.