CORS (Cross-Origin Resource Sharing) is a security feature that allows web pages to make requests to a different domain than the one it originated from. This feature is important because it allows web developers to build applications that utilize resources from different domains, such as API endpoints.

When a web page tries to make an API call directly from JavaScript, the browser enforces certain security measures to prevent unauthorized access. However, sometimes it is necessary to make these calls to different domains in order to retrieve other essential information via the use of AJAX calls. This is where CORS comes in.

The IP2Location.io Free plan does not come with CORS headers, which means that developers will need to wrap the API calls within their backend codes and re-invoke the API call from their own domain. This could result in additional overhead and impact the performance. However, by upgrading to the IP2Location.io Starter or higher plan, developers can take advantage of the CORS headers in the API response. This means that they can retrieve IP geolocation results directly from their web browser without additional wrapper calls.

Overall, CORS is an important security feature that allows developers to build more robust applications that can utilize resources from multiple domains.