This is the 5317th most frequent Dutch word.
koekkoek
"Cuckoo" (a type of bird).
Here 'koekkoek' refers to the cuckoo bird, typically known for its distinctive call.
Ik hoor een koekkoek in het bos.
I hear a cuckoo in the forest.
In this sentence, 'koekkoek' is used informally to address someone, often humorously implying they are not paying attention.
Koekkoek, ben je daar?
Cuckoo, are you there?
Here 'koekkoek' is used figuratively to mean something is crazy or unusual.