Does a Retrieve Job Have a Status of Pending?
If you initiate several concurrent retrieve operations for a single
org, Metadata API automatically puts some of those jobs in a queue, if that becomes necessary for
service protection. If a retrieve job has a status of Pending, it’s
in the queue. When one of the active retrieve jobs completes, Metadata API takes a pending job
from the queue and activates it. If a retrieve job has a status of
InProgress, it’s active. The process repeats until the job queue is
cleared.
For more information, see Metadata Limits in the Salesforce Developer Limits and Allocations Quick Reference.