A ream is a quantity of paper sold in a bundle, once comprised of 480 sheets but now rounded up to 500. If you write reams of love letters to your beloved, I hope she appreciates them. Or at least recycles.
The word ream has two distinct meanings, depending on whether you use it as a noun or a verb. As a noun, it refers to an amount of paper, its origin from the Arabic rizmah, or "bundle." As a verb, ream is a rough word that can mean "to make a hole in" or "to squeeze." When you "ream someone out" you give them a scolding.