Seats.io uses so-called hold tokens to keep track of objects that are temporarily held. This means the seat is marked as unavailable for a short while, until the person who selected it completes the ticket buying process.
Hold tokens are stored on the seats.io server until they expire. When a hold token expires, all associated held objects are automatically released.
Under normal circumstances, such a hold token is generated by the user's browser, when it renders a floor plan that has
session: 'start' or
However, you can also generate hold tokens programatically. This is useful when book best available seats via the seats.io API instead of showing a floor plan to your ticket buyers, but still want to take advantage of temporarily holding objects.