A bankroll refers to the total amount of money that a player is able and willing to stake out into the game. It is a term used to calculate the chips wagered by a player during a game. A lot of poker players like to keep their bankrolls apart from other funds they have instead of putting everything at risk. A playing bankroll that is adequate for a specific poker game is the amount of money that is sufficient enough to withstand all expected and unforeseen swings which may arise due to variance. This is also assuming there is a positive outcome.
For a game with a negative expectation, having a bankroll that is enough is one that does not run dry before the unexpected happens. Many poker players do limit their level of risk based on every session, in effect they play with bankrolls with each session. Whether a bankroll is generally meant for poker or not largely depends on how best they can manage their money. To bankroll a person means to provide part or all the funds they need to gamble. This also bestows part of the risk on you in return for some of the profit too.