A message is enqueued when it is in the queue (it was sent by the producer and it is waiting to be consumed).

A message is pending when a consumer is processing it. It is still in the queue, but not visible to other consumers for a limited time. The message is then either dequeued (it means: successfully processed by the consumer) or enqueued again.

The number of pending messages should return to 0, while the number of messages enqueued and dequeued should gradually rise and ideally be the same for a queue.