The iPhone X comes with dual rear cameras: A standard wide-angle camera and a telephoto camera. The telephoto lens on the X has an aperture of f/2.4, compared to f/2.8 on the telephoto lens of the iPhone 8 Plus.
A new feature on both the iPhone 8 Plus and iPhone X is Portrait Lighting, which allows you to sculpt lighting to best fit your subject. It isn't a filter, but rather does a real-time analysis of lighting on your subject's face.
The iPhone X uses what Apple calls a True Depth camera to unlock your phone with Face ID. The same camera can work alongside the front-facing camera to allow Portrait Mode and Portrait Lighting for selfie photos.