Your betting bankroll is how much money you have reserved for wagering. A betting bankroll is just for that: betting, not rent or bills or food. Make sure your betting bankroll is money you can afford to put at risk.
Do not bet your entire bankroll on one wager or one event. Betting is by nature volatile: even the best bettors don’t win every single wager. It is generally a good idea to keep bets between 1% and 5% of your betting bankroll: big enough to make meaningful increases to your bankroll when you win, but small enough that you have plenty of bankroll left to pursue good betting opportunities whether or not you win or lose.