Alpha characters, also called alphanumeric characters, are made for computers. They are made up of the 26 letters of the alphabet and the 10 Arabic numerals. Alpha characters also include different versions of letters for languages besides English.
Most of the time, what an alpha character is used for tells us what its parameters are. When naming files, only letters and numbers can be used as alpha characters. In programming, however, symbols are often used as alpha characters. This could be because, depending on the application, different subsets of alpha characters were used to keep people from misinterpreting them. Seat maps on planes are a good example of this. The letter “I” is left out so that it doesn’t look like the number “1.”