Some people may be confused with the USTA league ratings (1.0 to 7.0) so here is the unofficial guide.
1.0 - You stink. Your grabbing the wrong end of the racquet and you
think the green fuzz on the ball has something to do with velcro.
1.5 - You still stink, but you can tie your own tennis shoes and hit a
ball you have got in your hand towards one of the cardinal points
without hitting yourself in the leg.
2.0 - You have taken a few lessons, and the odour is fading. Your strokes
begin to look less like a grandmother waving a flyswatter at a moth
and more like you are actually trying to accomplish something.
2.5 - This is when you start going to the club round robins, and
discover that despite your previous misconceptions, you still stink.
You are doing alright if you are fed the ball, but everyone else is
really just being nice to you until they can win the point without
3.0 - Same as 2.5, but with more topspin.
3.5 - The light is dawning. Your feet begin to move more efficiently.
They do not remain glued to the baseline, but begin to move
around the court, even up to the net on those occasions that you
feel like walking back to the fence to pick up the ball that passed
4.0 - Your discovery of how to hit a serve and overhead allows you
to be one of the people politely destroying 2.5 players on
round robin night.
4.5 - The ball goes where you will it to go, with authoritative pace
and spin. You are king. You are undefeated on Round Robin night,
and wish test your mettle with a greater challenge. You ask
to play a match with your club's top players and after getting
your ass whupped that, in fact, you stink. "But", the Div 1 team
says magnanimously, "You are getting better."
5.0 - Around now, pretty much everyone else at your club stinks.
League play is the only way to get a decent match, and you're
starting to think pretty well of yourself.
5.5 - You crush some 5.0 punk in a league match, and tell him
6.0 - Tennis scholarship. You go to Stanford, play for the university
team, and have some sixteen year old prodigy bagels you in
a practice set and tells you you stink.
6.5 - You are offered a berth in a local ATP qualifier, and lose out
in the pre-draw round robin stage. One of the people in the
audience played tennis with you back in round robin, and he
tells you that you looked pretty good out there, but your
backhand still stinks.
7.0 - The pro level. You got to this level by yelling at referees, match fixing or taking drugs.
(I found this online, I don't know who to give credit to but very funny.)