The bankroll: a separate budget
The bankroll is the budget set aside for betting. It is kept apart from everything else: it is never mixed with the money you live on.
Never the rent
Nor the bills, nor the shopping, nor anything needed for everyday living expenses.
Never savings
Nor anything put aside for a plan or for the unexpected.
Only what you accept to lose
The basic rule: only put in what you accept to lose entirely, without it changing your life.