A mobile device is essentially a handheld computer. Although the category of mobile device might seem to include any electronic device small enough to be carried around, the term implies wireless communications and the capacity for general computing.
Currently, the most common examples of mobile devices are tablets, smartphones and e-readers. Within the enterprise and in the context of mobile device management (MDM), laptops are also included in the category because they are portable, employees use them in similar out-of-office locations, and they involve similar oversight and security requirements to those of smaller devices. Outside of this context, however, the category of mobile device is generally confined to smaller form factor devices.
The first mobile device, in this sense, was the personal digital assistant (PDA). Popular in the 1990s and early 2000s, PDAs are considered the precursors to smartphones. However, because they could not make phone calls, they were more like a very small tablet. Most PDAs had a physical keyboard and limited software. Some had an electronically sensitive pad for written input.
The size of a mobile device necessarily involves compromise between the functionality of a larger interface and the ease of carrying a smaller device. The phablet was designed larger than a smartphone for ease of input but smaller than most tablets, to fit in pockets and purses. The devices also include the phone function ordinarily lacking in tablets.