The mandible are set back more behind than the upper maxilla.
This is the typical orthodontic patient whose front teeth may stick out and over the lower lip and it gives the patient what is known as a bird profile.
It is usually accompanied by a lot of problems such as functional problem with swallowing, chewing, and sometimes speech. But also very frequently with jaw joint popping and inability to chew properly.
In some cases, if the retrusion is very defined it is common to perform a chin augmentation as well to provide better balance to the facial features.