Stoma (Greek 'a mouth')is the medical term for an artificial opening between two body cavities or between a body cavity or passage and the surface of the body. This opening is created in a procedure called an -ostomy.

For example, a tracheal stoma is an opening between the trachea and the body surface that is created during a procedure called a tracheostomy. Quite often, the specific opening will also carry the name of the procedure, i.e. the stoma created through a tracheostomy is a tracheostomy. The stoma created through a colostomy (creating an opening between the colon and the body surface) is a colostomy.

Not all stomata (or stomas, either is correct) are permanent; for example, a tracheostomy may be used for better medical effect and comfort in a patient who needs to be intubated for a long time, and then, once the patient is extubated, the stoma may be obliterated, leaving only a scar. A colostomy may be used in a patient who needs intestinal surgery, but after the intestines heal an end-to-end anastomosis may be performed, allowing normal intestinal function again.

Stomata, being artificial openings, require special care specific to the type of stoma. Stomata of the excretory organs generally require some type of drainage pouch and skin barrier, other stomata, such as respiratory or gastric, need other types of care.