# Week 13 - CORS in Detail
# Cross-Origin Resource Sharing
Cross-Origin Resource Sharing (CORS) is the name of a set of rules that Browsers use in determining whether assets from other origins or domains are safe to downloaded or use.
There are Request headers and Response headers that are only allowed to be set by the browser or the server. There are others that we are allowed to dynamically create or edit with JavaScript.
Sometimes a file can be fetched but we are not allowed to use the contents.
There are special requests called preflight requests that are used to determine whether these rules are met.