Menpo

"Me no shita men", generally known as menpō (or membō) is a half mask covering the face below the eyes and including the nose. It is worn with a samurai kabuto helmet. Menpo take many forms. They may be made from leather or metal, sometimes have a lacquered finish, and can include a variety of facial details such as mustaches.

Menpo means "face and cheek".

There are other kinds of masks that can be worn with a kabuto:

"Happuri" A whole face mask with center opening for the nose eyes and mouth,
"Hoate" The mask protects only the cheeks.
"Somen" (Entire Face) A mask covering the entire face.
"Hanbo" "Hambo" Half mask, covering the chin, jaw and sometimes cheeks.

Multiple sources