Seat Blocking?
 

Hello

What means "Seat Blocking" by airlines?

Airlines often will block access to reserving certain seats or a certain amount of seats until the day of the flight. One example is bulkhead seats which are often where travelers with infants are put for easier access & bassinets. Some other "preferred" seats can be blocked until the day of travel too.

"Seat blocking" also refers to the practice of trying to leave an empty seat next to a passenger unless the plane becomes quite full.