A digital device is an electronic device which uses discrete, numerable data and processes for all its operations. The alternative type of device is analog, which uses continuous data and processes for any operations. Any device which uses a computer of any sort in its operations is at least partially digital.
An ever-growing number of devices use digital technology, despite the fact that the world itself is largely analog in nature. For instance, if a dog jumps, it could jump a yard, just a foot, or literally any fraction of the distance between. If the world were digital, there would be some minimal unit, say, a sixteenth of an inch, which would be the minimum amount moved, and any movement would be some multiple of a sixteenth of an inch. In the same way, any product of a digital device will fall into one of a set number of possibilities, although these possibilities are often so numerous a human could not tell the difference.
Another example is the vinyl record compared to the compact disc. A vinyl record is an analog recording device. It records sound at exactly the time it is detected. A CD, on the other hand, records sound at the best approximation of the time it's detected that's allowed by its discrete storage units. While in some ways less precise, such recording is far more compact and, in most cases, is undetectable by humans.