The poker term freeroll most commonly refers to poker tournaments that don’t have any buy-in and is free to enter.
For example, freeroll tournaments can consist of players who entered an event for free during a poker room promotion or have received invitations to participate without having to pay any fees.
When used as a noun, freerolling refers to a situation in which you have the same hole cards as your opponent with a re-draw to a better hand, meaning that you can only tie or win.
Consequently, you’re freerolling because you’re not risking anything by sticking with your hand until the end.
For instance, let’s say both you and your opponent are all-in on the flop of JcTs9s. He is holding offsuit KhQd for a nut straight, and you have KsQs suited. Both you and your opponent have a straight after the flop, but you also have a redraw with a chance of hitting a flush. In this case, you will either win the pot if another spade comes or spit it with your opponent, making you freerolling in this situation.