When developing using Sitecore headless SDKs, what is the relationship between the rendering host and...

 Sitecore headless development is based on a decoupled architecture where the rendering host is a separate application that handles the presentation logic and the Content Delivery role is a Sitecore instance that handles the content management and delivery. The rendering host communicates with the Content Delivery role using Sitecore headless services, which are APIs that expose Sitecore content and layout data in a JSON format. The rendering host translates a visitor request to a content item in the Sitecore instance. The Sitecore instance using Sitecore headless services returns the content item and the associated presentation details, and so on, to the rendering host. The rendering host renders the content item for the visitor. This way, the rendering host can use any technology or framework that supports HTTP requests and JSON parsing, such as ASP.NET Core, React, Angular, Vue, etc. References:

Headless development with the ASP.NET Rendering SDK

Sitecore Headless Development FAQ

Sitecore Headless Development