The esophagus, oesophagus, or gullet is the muscular tube in vertebrates through which ingested food passes from the mouth area to the digestive system. Specifically, in mammals, it connects the pharynx, which is the body cavity that is common to the digestive system and respiratory system behind the mouth (buccal cavity), with the stomach, where the second stage of digestion is initiated (the first stage of digestion is in the mouth, with teeth and tongue masticating food and mixing it with saliva).
The junction between the esophagus and the stomach is not actually considered a valve, although it is sometimes called the cardiac valve, cardia or cardias, but is actually more of a stricture. Many people experience acid reflux, where stomach acid gets pushed up into the esophagus, causing a burning sensation, commonly termed heartburn.
Some people also experience a sensation known as globus esophagus, where it feels as if a ball is lodged in the lower part of the esophagus.
See also: achalasia