ELI5: Explain Like I'm 5

Product requirements document

A product requirements document (or PRD) is like a blueprint for a product. It lists out what a product should be and do. For example, if you are making a new toy car, the PRD might say that it should have four wheels and have a engine that runs on batteries. By writing out what the product should be and do, everyone involved in making the product can make sure they understand what will be needed to make it.