> 1. Used as the object of a verb to indicate an indefinite quantity; of it, of them. Replaces the partitive article (du, de la, etc.)
Tu as combien de livres ? J'en ai trois. — How many books do you have? I have three (of them).
Y a-t-il beaucoup de pièces ? Oui. Il y en a beaucoup. — Are there many rooms? Yes, there are many (of them).
Martin a trois sandwichs, mais j'en ai seulement deux. - Martin has three sandwiches, but I have only two (of them).
Il y en a combien ? - How many of them are there?