Ban evading is when you have an account on the same IP as an account that has already been banned.
Sometimes people don't actually ban evade, however, because their account is on the same IP as another persons account who has been banned, then they too must suffer the consequences even though it was not their doing. A good example are university campuses.
If you've never made an account that's been banned on Sythe before, then you should have nothing to worry about.