Quoting from here:
InFlightCount: The number of messages that have been dispatched and are
currently awaiting acknowledgment from the consumer. So as this number
decreases, the DequeueCount increases.
AverageEnqueueTime: On average, the amount of time (ms) that messages
remained enqueued. Or average time it is taking the consumers to
successfully process messages.
EnqueueCount: The number of messages that have been written to the queue
over the lifetime of the queue.
DequeueCount: The number of messages that have been successfully (i.e.,
they’ve been acknowledged from the consumer) read off the queue over the
lifetime of the queue.
DispatchCount: The number of messages that have been dispatched (sent) to
the consumer over the lifetime of the queue. Note that dispatched messages
may not have all been acknowledged.