Chess.com rating is a measurement of "competitiveness" of the player.
It does not measure how much knowledgable about chess the person is nor how clever or intelligent someone is!
It can be affected by many factors: like how serious the player is with the game, how many concurrent games, whether chess books is used, whether the person sets up a chess board, whether any stress or emotional pressure is on him/her etc.
It does not translate to USCF or FIDE ratings. I would like to do some study regarding it but I believe there is no correlation. OTB ratings is not updated as much as chess.com ratings, has faster time controls, more pressure, more serious attention by chess competitors and more evenly spread of white-black games. Besides, one doesn't have any choice in the opponents one play at OTB.Whereas in chess.com I can reject opponents to play or select min/max ratings of chess opponents.
What does the chess.com rating really mean? Is it a "real" rating? Does it translate to USCF or FIDE in some way? or is it just for this website? I'm talkign about the rating number you get from just training classes...not playing online games.