This will go into detail far more than I can in a post. http://www.subbu.org/blog/2008/04/nouns-and-resources but the tl;dr is REST nouns are a construct in which you identify all of your objects in a system, these become your REST endpoints such as User in which you have GET, POST, PUT, DELETE each of these verbs causing a specific action on the object or noun. This works great for a large portion of the application but there are some areas such as transactions where it is very hard to logically turn the action into a noun and make it understandable. Sometimes we need the back end to orchestrate multi-step actions and the noun construct just does not convey the workflow. When this happens some people choose to use verb systematic such as generatePDF while still maintaining the REST HTTP actions while others tend to strictly adhere to making said process a noun which can effect readability.