When a poker player announces that he is going "all-in" it means that he is betting all the chips that he has at the poker table at that moment.
Going all-in is a strategy used by a lot of no-limit poker players in order to place a lot of pressure on their opponents. It is an extremely aggressive move, unless you happen to be short-stacked in which case it will be interpreted as a desperate move (which it usually is!) and your opponents will be happy to call you down.
If you have a lot of chips, however, then an all-in bet is very difficult for an opponent to counter unless she happens to have a monster hand.
