If you have ever seen the BACKUPTHREAD wait type in the sysprocesses table or sp_who2 output and wondered what it is, I have found the answer.
The basic explanation is “Used when waiting for a backup thread to complete. Wait time may be very long (minutes, hours).” Basically what this means is that there is a backup running and something is waiting for it to complete.
When i saw this show up I was running a restore. That restore had three entries in the sysprocesses table. The first was the main kpid, with two child kpids. The parent kpid was the wait type of BACKUPTHREAD while it was waiting for the child kpid to finish processing. In my case the wait time was short, and it seamed to switch from this wait type to an IO wait type.