This is a count of jobs waiting in symbiont queues that are submitted but not yet ready to be processed by the output symbiont, the process responsible for actually delivering queued output to a device. A rising pending count suggests output is backing up before the symbiont picks it up, which can point to a symbiont that is busy or delayed. For example, several jobs submitted to a shared output symbiont while it is finishing a large prior job would appear here as pending.