Ream is a word with two distinct meanings:

1. A standard quantity of paper, equal to 500 sheets. When your teacher orders paper for the classroom printer, it usually comes in reams. Before computers, offices would go through reams and reams of paper for letters, reports, and records. If you've ever bought printer paper at a store, you've probably seen it sold by the ream. The word helps people buy and sell paper in predictable amounts, just like eggs come in dozens.
2. To criticize someone severely or harshly. If a coach reams out a player for not following the game plan, they're delivering a serious scolding. When someone gets reamed for turning in sloppy work, they're receiving sharp, pointed criticism meant to correct their behavior. This usage is informal and suggests the criticism goes beyond gentle correction. It's the difference between “Please try harder next time” and a much sterner conversation about poor effort or careless mistakes.