noun
unoccupied seat; unreserved seat
Refers to a seat that is still available, either because it has not been reserved or because no one is sitting there. Often used in the context of events, transportation, or classes.
この公演にはまだ余席があります。
There are still seats available for this performance.
余席が少なくなってきたので、早めに予約してください。
Remaining seats are becoming limited, so please book early.