How to understand Github Action Status Queued?

I’ve noticed that when a Github Action trigged, the workflow in the status Queued.

I want to know why it’s queued?

Are there any docs about it?

It is queueing up waiting for a runner to become available. Especially with hosted runners, while we have a lot of them “in the pool”, sometimes it can take up to a minute for one to be allocated and assigned.