Burn cards are card discarded before dealing from the deck. This is standard procedure for proper dealing, which is designed to prevent cheating.
It is possible for a corrupt dealer to flash the top card to a confederate by sliding it to the side and rolling the deck. Alternately, if a deck becomes worn and recognizable marks appear on some cards, some players may be able to identify the top card, giving them an advantage. Consequently, the top card is always discarded before dealing out rounds of cards between rounds of betting.