Rolling is the live sparring portion of BJJ training where both partners resist and respond freely, as opposed to drilling where one partner is compliant. A standard roll lasts five to ten minutes; most classes end with several rounds.
Rolling is where BJJ skills are tested and built. Techniques you can drill perfectly often break down when the opponent is resisting and moving. Rolling pressure-tests your game and reveals gaps — positions you don't know, timing you haven't developed, submission defences you assumed you had.
Beginners often find rolling overwhelming at first. The advice given in most academies is to focus on surviving and getting comfortable rather than trying to submit everyone. Over time, the chaos resolves into positions you recognise, and your toolbox expands from there.
A roll ends when time runs out, when someone taps, or by mutual agreement.