In Sitecore, the content delivery role and the rendering host are two separate concepts that work together to serve content to website visitors.

The content delivery role refers to the server or servers in a Sitecore environment that are responsible for delivering content to website visitors. These servers handle requests from users, retrieve content from the Sitecore database, and render the appropriate web pages or components. The content delivery role is typically separate from the content management role, which is responsible for authoring and managing content within the Sitecore platform.

On the other hand, a rendering host is a logical representation of a server or servers that can render Sitecore components. A rendering host can be associated with one or more content delivery servers. It is responsible for executing the rendering logic defined within Sitecore items, such as renderings, sublayouts, or view renderings, and generating the HTML output that is sent to the website visitors.

The rendering host can be configured to control the execution environment for the rendering, such as the server's operating system, version of .NET framework, caching settings, and other factors that may impact the rendering performance and behavior.

So, the relation between the content delivery role and the rendering host is that the content delivery servers handle the delivery of content to visitors, while the rendering host executes the rendering logic and generates the output for the components displayed on the website. The rendering host is typically configured on the content delivery servers to ensure proper rendering and performance.