Function buttons are specific buttons on a device or machine that perform a particular task or action. They are designed to make it easier for us to use or control the device without having to navigate through menus or settings. Full definition
There's also a full run of function buttons on board to change volume, brightness and so on. (pocket-lint.com)
A couple of function buttons are positioned to the right of the display and a heart rate sensor sits beneath the display, as it did on the previous model. (pocket-lint.com)
We appreciate that users have the ability to customize which functions these buttons perform. (laptopmag.com)