dead card; cards not in play
In competitive karuta, cards that are not present on the field at the start of a match, typically because they have been removed or are not part of the current set.
If a dead card is read, please withdraw your hand immediately.
In this match, there are three dead cards.
Compound of 空 (から, 'empty') and 札 (ふだ, 'card'). The reading からふだ is a straightforward combination.