ASCII stands for American Standard Code for Information Exchange.
The purpose of ASCII is to create a standard for
character-sets used in electronic equipments. The standard ensures that
different devices (which might be manufactured by differing companies) can communicate to each other with the same
character-code. With this kind of standardization,
programmers and computer manufactures will be "on the same page".
Imagine the problem if MAC and PC have different keyboard codes. The
standard ASCII character-sets not only includes all the alphabetical letter and
numbers, but also punctuations.