む, in hiragana, or ム in katakana, is one of the Japanese kana, which each represent one mora. The hiragana is written with three strokes, while the katakana is written with two. Both represent [mu͍].
In the Ainu language, ム can be written as small ㇺ, which represents a final m sound. This, along with other extended katakana, was developed by Japanese linguists to represent Ainu sounds that do not exist in standard Japanese katakana.