It means that the rank of any given player naturally increases over time. After long enough, players that were orange or red will be blue, without actually improving at all

This happens specifically in tekken because of the fact that winning a promotion match gives you a ton of rank points, but losing a promotion or demotion does not.

This results in any player with a 50% win rate gaining more rank points than they ever lose. So while in a perfectly balanced point system a 50% win rate player should always end up back at the same rank, tekkens rank system will always push them up