noun
how many; how many pieces
Used to ask about the number of small, countable objects. The counter 個 is general and can be used for many items when a specific counter is not required.
りんごは何個ありますか。
How many apples are there?
この箱の中にボールが何個入っていますか。
How many balls are in this box?
Combination of interrogative prefix 何 (なん, 'what') and counter 個 (こ, 'individual item').