Definition of level
The term level is mostly used in tournaments. A tournament is divided into levels. Depending on the structure, the tournament can have level, 50 or 100 levels. The tournament starts at level 1, and the level 1 will be 15 minutes long. During this time, the blinds will be at levels/50 without ante. After 15 minutes of play, the level 2 will have bigger blinds's. The level 2 will have bigger blinds's. With each new level in tournament, the blinds will increase. So for the level 2, let's say that the blinds's will now be 50/100. So on and on until there is only one player left in the tournament.
Always be on the lookout for the levels in the tournament.
It's important to keep the levels in mind when playing tournaments because depending on the level, it can alter your style of play. Let's take a concrete example to understand. You have 15 big blinds in a tournament in position cutoff. You receive an average starting hand. You hesitate to open it. With 15 big blinds, it's difficult to raise-folder so you're thinking about pushing all in, but you're not sure. If the next level comes up very soon and the raise of blinds will give you 8 big blinds instead of 15, it might prompt you to play your hand.