In the most general sense, think of digital as a form of representation in which distinct objects (or digits) are used to express something in the real world (for example, time or temperature). That way, counting and other operations can be performed precisely. When data is represented digitally, it can be manipulated to produce a calculation or some other computation, such as a picture.
In the technical sense, digital describes electronic technology that generates, stores, and processes data in terms of two states: positive and non-positive. Positive is expressed or represented by the number 1 and non-positive by the number 0. Thus, data transmitted or stored with digital technology is expressed as a string of 0's and 1's. Each of these state digits is referred to as a bit (and a string of bits that a computer can address individually as a group is a byte).
Prior to digital technology, electronic transmission was limited to analog technology. Digital technology is primarily used with new physical communications media, such as satellite and fiber optic transmission. Other examples of digital media include CDs, Zip Disks, and hard drives. Generally, telephone lines transfer analog information (sound waves), whereas modems transfer digital information (1's and 0's). Post digital? It's VoIP.