How does a 403 Forbidden error differ from a 401 Unauthorized or 404 Not Found error?

A 403 Forbidden error means access is explicitly denied by the server, regardless of authentication. A 401 Unauthorized error indicates that authentication is required to access the resource, and the client needs to provide valid credentials. A 404 Not Found error means the server cannot find the requested resource at the specified URL, implying the resource simply doesn't exist or the URL is incorrect.