The phrase "metal backs" refers to objects or products that have a backside made from metal instead of another material like plastic or fabric. Full definition
You especially notice how good it appears when looking at the all - metal back of the phone. (techradar.com)
It not only looks great, with illuminated keys and a brushed metal back drop, but it's also highly customizable and responsive. (heavy.com)
The handset is reasonably ergonomic, though as the matte metal back panel is somewhat slippery, you'll need to keep a firm grip on the handset during use. (techspot.com)