a player is called to take a seat but is momemtarilly unavailable. If known by the house, his/her seat will be reserved until he/she returns. Also used when a player leaves the table, another seated player wants that empty seat, but because of the blinds, he/she remains at the old seat for a couple of more hands. The "button" keeps a new player from taking the seat.

Talk about a versatile chip!

Jim