Quick answer
Miku is a girl name.
Meaning and history
From Japanese 美 ( mi ) meaning "beautiful" combined with 空 ( ku ) meaning "sky" or 久 ( ku ) meaning "long time". It can also come from a nanori reading of 未来 ( mirai ) meaning "future". Other kanji combinations are possible as well.
Notes and context
Usage: japanese | Japanese Hiragana: みく; Japanese Katakana: ミク