M21 or M-21 may refer to:
==Transportation== M21 (New York City bus), a New York City Bus route in Manhattan M-21 (Michigan highway), a road connecting Flint and Grand Rapids M21 (East London), a Metropolitan Route in East London, South Africa M21 (Pretoria), a Metropolitan Route in Pretoria, South Africa M21 (Durban), a Metropolitan Route in Durban, South Africa Highway M21 (Ukraine)
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).