Yeah, basically Same-Origin Policy (https://en.wikipedia.org/wiki/Same-origin_policy) was the part that increased security, as it prevented websites (in browsers) from making arbitrary requests to arbitrary 3rd party websites.

Cross-Origin Resource Sharing (https://en.wikipedia.org/wiki/Cross-origin_resource_sharing) is one way to relax the Same-Origin Policy, so you essentially whitelist what actually can be shared across Origins. To be used when the default Same-Origin Policy is too strict.

Overall I think it's a really simple concept, but libraries/frameworks/docs seems to constantly over-complicate it with their explanations.