The term blank in poker refers to a community card that is highly unlikely to significantly impact players’ holdings or change the action.
For example, on a board of Kh6hJc, a 3s coming on the turn is a complete blank. This card doesn’t work with any of the flop cards in any significant way and it is unlikely to change the strength of hands of players involved in a pot, especially if there was any betting on the flop.
Of course, whether a particular card is a blank or not is defined entirely by the board texture. There are no cards that are inherently blanks. The same 3s from the previous example would be very meaningful after the flop As2s5d.
