Queue is what the notifications show for posts pending approval in the Review Queue. I see it a lot on my instance where we lock users to TL0 to force mod approval of their posts before using silences/suspensions.
Depending on the value of the auto handle queued age setting they either remain in the queue until handled (set to 0) or they get rejected automatically > 0.
That setting also affects other flag types as the description mentions:
Automatically handle records that are waiting to be reviewed after this many days. Flags will be ignored. Queued posts and users will be rejected. Set to 0 to disable this feature.