Fifth street is a poker term used to refer to a specific stage in a round of poker.
In a game of poker, apart from receiving cards that are dealt face down, players can often make use of the community cards, depending on the variance of poker they are playing. Community cards are dealt face up and are displayed in the centre of the table. Players can then use them in combination with their cards to form winning hands.
If you are playing Texas Hold’em, during the fourth round of betting, there will be five community cards on the table. For that reason, many poker players refer to the fourth round of betting as the fifth street. However, keep in mind that some players may refer to that round as the river.
If you are playing a game of Seven-Card Stud Poker, for example, during the third betting round the players will have four cards in their hands — two hole cards, a face-up door card, a face-up fourth street, and a face-up fifth street.