Antrum

In biology, antrum is a general term for a cavity or chamber, which may have specific meaning in reference to certain organs or sites in the body.

In vertebrates, it may refer specifically to:
 * antrum cardiacum, a dilation that occurs in the esophagus near the stomach (forestomach)
 * antrum follicularum, the cavity in the epithelium that envelops the oocyte
 * mastoid antrum, a cavity between the middle ear and temporal bone in the skull
 * pyloric antrum, the initial portion of the pyloric part of the stomach. This is what is usually referred to as "antrum" in stomach-related topics.
 * maxillary antrum or Antrum of Highmore, the maxillary sinus, a cavity in the maxilla and the largest of the paranasal sinuses

In invertebrates, it may refer specifically to:
 * antrum of female lepidoptera genitalia