Definition of freeroll
A freeroll has several meanings. A freeroll can be a free entry in a contest or lottery. If you find a lottery ticket on the ground and the draw is coming up, you have a freeroll. Your participation cost is 0 and you have a potential future win. In poker, a freeroll can be a tournament for beginners. Some poker rooms will offer beginners free tournaments with freeroll0 euros in prize money (more or less freeroll0 euros, depending on the tournament). They will be called freeroll tournaments.
A freeroll on a stack game
You can also talk about freeroll when you, like your opponent, have a made hand, but in addition, you have a draw. Imagine a 3bet pot in which you have AK in your heart. Your opponent has AK in spades. flop falls A-2-5 with 2 hearts and you are all in at flop. In this case you have a freeroll because your odds are 0. In the worst-case scenario, you will win half the pot and if you hit your draw, you will win the entire jackpot. Having a chance to win a prize with no cost or no future loss is a freeroll.