Chess Odds of Winning..?


I realize that the numbers at the top corners, that fluctuate during a game on chess.com, indicate who is currently considered to be winning (+ white is winning, - black is winning)...but what exactly do the numbers mean.
I realize that the numbers at the top corners, that fluctuate during a game on chess.com, indicate who is currently considered to be winning (+ white is winning, - black is winning)...but what exactly do the numbers mean.