hundreds of items; a large number of things
Used to emphasize a very large quantity of countable objects. The reading なんびゃっこ is a contraction of なんびゃくこ.
Hundreds of cardboard boxes are piled up in the warehouse.
He collects hundreds of marbles.
何百 means 'hundreds' in a general sense, while 何百個 specifically counts individual items.
数百個 also means 'hundreds of items', but 何百個 is more colloquial and emphatic.
Compound of 何 (nan, 'what') + 百 (hyaku, 'hundred') + 個 (ko, counter for small items). The reading なんびゃっこ results from rendaku and contraction.