How can I tell if a website is using a Hybrid Web Design approach?

Based from what I've read, there are 2 common types of Website Design: responsive and separate desktop & mobile sites. Then, there's the hybrid that combines the two.

It's easy to distinguish a responsive website by resizing the browser. A website that uses "separate desktop/mobile approach" can be distinguished easily if the user is redirected to another site, similar to Facebook that redirects the user to "m.facebook.com".

Now what confuses me is identifying a hybrid website. How can one tell that the website is Hybrid?