A cuckoo clock is a kind of clock. Cuckoo clocks have a wooden case that looks like a small house, and there are wooden doors that open. It gets its name because at the start of every hour, the small doors on the clock open up and a little wooden bird comes out of the door. The clock then makes a noise which sounds like a bird call ( "Koo-Koo" or "cuckoo").
The clock makes the sound one time for each hour it is. Whether it is morning or night does not change the number of times the bird makes the sound.