This tag is used when an esophageal sphincter is depicted, usually in but not limited to vore.
There are two esophageal sphincters found in a mammalian body, an upper and a lower.
They are between pharynx and the esophagus and between the esophagus and the stomach.
If the opening to the stomach is an open tube with no indication of a sphincter don't add this tag.

Related tags

inside_stomach, vore, internal, stomach.