In poker, it’s important to be properly bankrolled for the games you play. A failure to play within your roll will put you at risk of going broke, which is bad not only because it means you’ve lost a lot of money, but also because it means you won’t be able to continue playing.
Your bankroll is all the money you have available that you’re willing to spend on playing poker. If you have balances at five different sites, then it is the sum of all those different account balances that is your bankroll. Similarly, if you have $100 on one of the sites but you’re willing to deposit another $400 without any problem, then your bankroll is $500.