Probability is a huge factor in texas hold 'em. Players use odds to determine their actions. The chances of finishing a flush or a straight, the probablity of getting an overcard, the percentage of times you're going to flop a set to match your pocket pair are all important factors in poker. Knowledge of these statistics is key to winning. In online games especially with very few (if any) tells, statistical knowledge becomes the main factor when choosing whether to bet, call, or fold.

Here are some terms that you'll hear on this site and whenever you're talking about poker odds...
Outs The number of cards left in the deck that will improve your hand.
"I had four hearts on the turn, so I had only 9 outs left to finish that flush."
Pot Odds The odds you get when analyzing the current size of the pot vs. your next call.
"There's $200 already in the pot, and only another $10 bet coming at me, so my pot odds are good if I hit that flush."
Bet Odds The odds you get as a result of evaluating the number of callers to a raise. "With a 1 in 5 chance of hitting it, and knowing all six of these guys are gonna call my bet, my bet odds are good too."
Implied Odds The odds you are getting after the assumed result of betting for the remainder of the hand. "Since I think these guys are going to call on the turn and river, my implied odds are excellent."
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