A bankroll, also known as a "betting bank", is the amount you're willing to invest in your betting.
It's from this bankroll that you'll allocate an amount to each tip, as set out in the staking plan.
It's important that you start with an amount that allows you to take a long-term view.
Your bankroll should be an amount that's set aside from your other day-to-day finances and savings, which will help keep emotion out of your betting.