A response header is an HTTP header sent by the server, along with a page resource.
The response header lets the server pass information to the browser that is related to the resource being sent, such as the resource’s file type, resource file size, which server/CDN was used to serve the resource, etc.
Click on a request on the Waterfall Chart to view its Response headers.
The response header also contains more information related to the server that sent the resource, as well as, additional details like how long the resource can be cached for, when the resource was last updated, etc.