'Hit & Run' is when a player joins a cash table with the minimum buy-in and leaves after winning a pot. It's not against the rules but it's considered bad manners.
If you win the pot with a short stack and leave the table, the next rule applies. To get back to the table within 120 minutes, you need to buy in with the same amount you left with or no less than 10% if that's all you have.
This policy applies to Pot Limit and No Limit games.