What does "pending publication" mean?

Pending publication is a later stage than pending review.

Once the editor of the journal thinks the manuscript is worth being reviewed, he dispatches it to the referees. From this moment until the decision letter is issued, the state of the manuscript should be Pending review.

Once the decision letter states that the manuscript has been accepted for publication (maybe after revisions, so it will be the last decision letter), the state of the manuscript becomes Pending publication. This usually corresponds to that short period allowed for proofreading and typographical adjustments.