drop-in

1. One who casually drops in (visits unannounced or without appointment).

   The office was efficient, but not well equipped to handle drop-ins.

2. An informal event that does not require booking in advance.

3. A place that can be visited casually, without an appointment.

4. The act of dropping in; that is, taking a wave that another surfer is already riding.

5. A pitch that is prepared away from the ground or venue, and dropped into place only when a match is to be played.

6. A message or advertisement inserted into other material.

regular