Before learning more about CORS, it's important to familiarize yourself with SOP (Same-Origin Policy).
What Is SOP (Same-Origin Policy)?
SOP is a security mechanism implemented in almost all of the modern browsers. It does not allow documents or scripts loaded from one origin to access resources from other origins. Now, what is the origin? The origin is not only domain. — the origin could be the combination of the Host name, Port number, and URI (Uniform Resource Identifier) Scheme.
