1. An artificial waterway constructed for use by shipping, for irrigation, or for recreational use.

A canal may take in parts of natural rivers along its course.

2. In astronomy, an indistinct surface feature of Mars once thought to be a system of channels; they are now believed to be an optical illusion.
3. A bodily passage or tube lined with epithelial cells and conveying a secretion or other substance.
4. An anatomical tube in the body, or a tube-shaped passage in the body, carrying air, liquids, or semisolid materials.
5. Etymology: from Latin canalis, "pipe, groove, channel"; from canna, "reed"

Originally it was "a pipe for liquid", its sense was changed in about 1673 to "artificial waterway".

A canal giving passage to a hernia.

The passageway for the hypoglossal nerve in the occipital bone (bone that forms the rear and the rear bottom of the skull).

A pathway from the mantle cavity through the funnel for water in cephalopods.

A short canal or opening between the stomach and the small intestine which is primarily consisting of muscle which can become too narrow, in some circumstances.

When the canal becomes too narrow, food and liquids may not be able to pass and this can result in symptoms easily feeling full, odorous belching, or nausea and vomiting.

A vertebral passageway containing the spinal cord and its membranes: Lumbar spinal stenosis is a widespread disorder that creates increased pressure or stress in the spinal canal.

A passage that extends into the elongated, flexible, arm-like extensions of an animal: Some invertebrates have tentacular canals in their tentacles; such as, "jellyfish" which are free-swimming marine animals consisting of umbrella-shaped bodies with trailing tentacles; and it should be noted that these soft-bodied animals are not fish.