Ostium

An ostium is a small opening or orifice, as in a body organ or passage.

It can mean the following

• Any of the small openings or pores in a sponge.

Anatomy

• Ostium of Fallopian tube.
• Ostium primum or foramen ovale (ostium secundum) of the developing heart.
• Ostium maxillare of the Maxillary Sinus