An orinasal mask is a breathing mask that covers the mouth and the nose only. It may occur independently, as an oxygen mask

Oxygen mask

An oxygen mask provides a method to transfer breathing oxygen gas from a storage tank to the lungs. Oxygen masks may cover the nose and mouth or the entire face...

, or on some anaesthetic apparatuses, or it may occur inside a fullface mask on a scuba set

Scuba set

A scuba set is an independent breathing set that provides a scuba diver with the breathing gas necessary to breathe underwater during scuba diving. It is much used for sport diving and some sorts of work diving....

 or an industrial breathing set to reduce the amount of dead space

Deadspace (in breathing apparatus)

Deadspace in a breathing apparatus is excess space which the flow of air or breathing gas must pass through and back again as the user breathes in and out, increasing the necessary respiratory effort to get the same amount of usable air or breathing gas, and risking accumulation of carbon dioxide...

. According to how it is designed for use its lower edge may seal on the front of the lower jaw or may go under the chin.