The word sheath has a number of related meanings in English. In general usage, a sheath is any protective covering that fits closely around the object to be protected. A sword's sheath is called a scabbard.

• A sheath (synonym: jacket) is the outer covering or coverings of a communications or power cable. It is made of tough material, often plastic, that is resistant to environmental hazards such as abrasion, liquid intrusion, solar radiation, etc., and is used to protect cable components such as optical fibers or metallic conductors that transport the signal or power.

There may be more than one sheath surrounding a given cable. For example, some cable designs use an inner sheath surrounded by metallic armor, over which is an outer sheath.

(Source: Federal Standard 1037C)

• Sheath leaves are a type of leaf characteristic of some monocotyledonous plants, especially grasses. Sheath leaves are typically long, narrow, and triangular in shape. The leaf veins are parallel. The main characteristic is a basal part (the sheath) that clasps the stem or culm for some distance above the leaf origin (node). An example of a plant with sheath leaves is maize.

• A sheath is another word for condom.

• A penis sheath is traditional clothing in New Guinea, worn without other clothing, tied in upward position (see image)

• A sheath is a pocket or covering of skin covering the penis of a canine or other mammal (see foreskin).

• The Debye sheath is the non-neutral layer several Debye lengths thick where a plasma contacts a material surface.