1. a large pile or quantity of sth
a mountain of work/forms
A ‘mountain’ of something is a large pile or quantity of something. This phrase is similar in meaning to ‘a heap of’ and is usually used to exaggerate the size or amount of something. You could have a ‘mountain of work’ to do or have a ‘mountain of books’ or other objects in your home for example. This is largely an informal expression.