A "freeroll" is a tournament with some prize, but no entry fee.

"freerolling" is when you have part of the pot locked up, and and have a chance to win the whole thing.

Ex: you have your opponent has

The flop is you have half the pot locked up, but are "freerolling" to hit your flush and scoop the whole pot.

Similar to hi/lo games where you have the low side locked up vs a high hand, and you have outs to beat his high.