noun

• (rail transport) The rails that a tram runs on.
• (tennis, Britain) Either of the two pairs of sidelines marked on a tennis court which mark the outside of the singles and doubles playing areas.
• (film) A scratch on a film, usually vertical, that extends through multiple frames.
• (medicine) A mark or bruise having the shape of two parallel lines.
• (lexicography, Oxford English Dictionary jargon) A pair of vertical bars (||) placed to the left of the headword in certain editions of the OED to indicate that the term is "alien or not fully naturalized" (such as a recent borrowing).