M line
M line may refer to:
- M-line (mittel line or middle line), a structure in a muscle sarcomere
- M Ocean View, a light rail and former streetcar line in San Francisco, California
- M-Line Trolley, a streetcar line in Dallas, Texas
- M (Los Angeles Railway), a former streetcar service
- M (SEPTA Metro), a light metro in Montgomery County, Pennsylvania.
- Geometric mean
See also
- M Train (disambiguation), several train services
- M1 (disambiguation)#Railways
- Line M (disambiguation)