1. A mark, strip, or streak. 2. Anatomy a long, narrow mark, strip, or streak distinguished from the adjacent tissues by color, texture, or elevation. 3. A unit of measurement used by histologists in the 19th century; it varied in different countries from one tenth to one twelfth of an English inch. 4. A laboratory derivative of a stock of organisms maintained under defined physical conditions. 5. A section of tubing supplying fluid or wire conducting impulses for monitoring equipment; intravenous line, arterial line, electric line.