It is a pet name with beautiful meaning in a Japanese word. It is meant to be used because the definition of it is beautiful and annoying at the same time.
So, next time when you get a pet just name it Miku...
1. M4A1 Sherman - A widely used American tank during World War II.
2. M4 Carbine - A short-barrel (carbine) version of the Colt M16A2 assault rifle. Used widely by law enforcement and special forces.