The Bar (or Slab, or Candybar) is a popular electronics form, where the device is a rigid cuboid. It is so-named because it resembles a candy bar or slab in size and shape. This form factor is widely used by manufacturers such as Nokia and Sony Ericsson.
It usually refers to mobile phones, but can be applied to the whole portable electronics industry. For instance, the PlayStation Portable game console is a slab console, while the Nintendo DS is a flip console.
The most common useage of the description is towards mobile phones. Slab mobile phones have the screen and keypad all on one face. Some phones, such as the iPhone, do away with the keys, in favor of a touchscreen.