Definition of auto-rebuy
The auto-rebuy feature at online poker tables is present in both cash games and tournaments. In tournaments, it is a box that you have to check that will say "auto-rebuy". This will tell the software that if you are eliminated from the tournament in a hand, you want to automatically buy in. If it is still possible to do so (some tournaments have rebuy-possible maximums), the software will automatically take the money from your balance and give you the starting chips back. In cash games, the auto-rebuy option will add back the blinds you lost in each hand (up to the table maximum).
Advantages of the auto-rebuy option
The advantage of this auto-rebuy option is especially for cash games. If you're the type of person who likes to multi-table at 8 or even 12 tables simultaneously, filling your stack to 100 big blinds every time you lose a pot can be very time consuming. It's best to let the software handle the situation. The auto-rebuy can be set to rebuy at the number of pre-determined big blinds, often 100. Good poker players will always want to have a full stack in cash games to maximize the size of the pots they win.