Poker is a strategy game that involves a huge deal of deception and intimidation. Since each player deals with incomplete information (one does not know what the other players are holding), one can only deduce the strength of the hand an opponent is holding through their game behavior and through poker mathematics.
We must add an emphasis on game behavior, since it would take a genius to be able to properly deduce an opponent's tendencies through computing for the probability of their hand. Thus, most poker players rely on observation: on observing physical behavior and betting behavior.
Table image is exactly the totality of those observations. In poker, table image simply means your own game tendencies as perceived by other players. These players will then most likely act according to the table image you evoke.
If you constantly bluff, for example, then your opponents will most likely call and raise you in order to spoil your attempts at bluffing. This is because your table image is that of a bluffer.
Keep in mind that table image is not your real tendency in playing. It is what your opponents perceive. And since your opponents will most likely act in reaction to your table image, then you could fake a table image to lure your opponents to executing certain acts.
Let us take the table image of a bluffer again as example. Since opponents will most likely call and raise against you, you could lure them into putting more money in the pot even when you are really holding a great hand. Thus, you don't need to slow play.
Another example of using table image as a deceptive device: if you come in at the casino and look as if you are a guest that's just passing your time, players will most likely not see you as a threat. Because of that, you will most likely be played aggressively against, since they will think that you are playing weakly.
Always remember that you are the only one who knows your real tendencies. One's table image could easily be the opposite of your patterns of behavior. If you play out of character, you could easily lure opponents into acting according to your whim.
A good understanding of the concept of table image will help you in executing great poker plays. Remember that poker is a game of deception. If you don't use that table image to trap your opponents, then expect to be trampled over. Fake that table image and you will surely milk your opponents out of their chips.