unreserved seat; non-reserved seat
Refers to a seat that is not assigned in advance, commonly used for trains, theaters, and events. Often contrasted with 指定席 (reserved seat).
See also: 指定席
The unreserved seats on the Shinkansen are often crowded.
I bought an unreserved seat ticket, so I lined up early.
I arrived early, so I was able to sit in an unreserved seat.
I used unreserved seating to avoid the crowds.
The unreserved-seating car is near the front of the train.
Since my plans changed, I switched from a reserved seat to an unreserved one.