CORS stands for Cross Origin Resource sharing. It’s a way for a server to allow pages hosted on other domains (technically other origins) to make http requests to it.

A web page can usually embed images, scripts, video, audio, etc. from any location it wants. However, web fonts and AJAX requests can usually only make requests to the same origin the web page is served from, because of the same-origin policy. CORS allows a server to mark resources as shared with other origins, by sending an Access-Control-Allow-Origin header in response to an OPTIONS request from the browser.

For information on how to set this up on your server, refer to this document.