Intuitive explanation on CORS with a lot of examples. The article is not short but the reading was fun.

There are these three types of CORS requests, embedding, reading and writing. Each are treated differently. CORS embedding controls cross-site resources to be embedded. CORS writing controls form. CORS reading controls the ability for a script to read the response from a cross-site request.

The article also explained how preflight request works, and CORS in local context, etc. Overall very nice to read.