A "shell case" refers to the outside covering or container of something, often made of a hard material like metal. It can be the protective covering of a bullet, the outer layer of a phone, or the metal casing of a device. Full definition
If so, then go grab a hard shell case for under four bucks. (phonenews.com)
This bag comes with a removable soft shell case for the handheld console, along with room to store a bunch of its accessories and the rest of the system. (imore.com)
They will be sending out a complimentary premium in - vehicle charger and a slide - out hard shell case as a thank you gift to their customers. (androidheadlines.com)