Disconnect protection is a measure whereby a player's bets in an online game are protected if his internet connection fails. The usual method is to treat such a player as all-in; he makes no more actions and participates in the showdown.
This function varies from platform to platform. Usually, there is a limit to the number of times this will work for a given player. Often it is not available in tournaments; the disconnected player's cards are folded and he loses the bets he's made so far.
These limitations are to prevent abuse of the feature, since a player could just disconnect his machine if the wagers become too high but he does not want to fold. Such disconnect protection abuse is seen as cheating by some platforms, but it is very difficult to prove.