What is a Pending ticket?
Marking ticket as pending is a way of signalling that more time is needed for it to be resolved. When a ticket is marked as Pending, it's SLA timer is paused. This provides the agent responsible for this ticket with more time to find a solution.
It is not necessary for a ticket to be marked as Pending during it's lifecycle, as it may be solved immediately and therefore marked directly as Resolved.
LiveAgent doesn't have this feature yet.