Character
A character is a block of information that corresponds (usually) to a written character.
Originally, each character was typically stored in a single 6-bit byte; later, 8-bit bytes were used almost exclusively (to the point where 'byte' and 'character' were virtually synonynms).
The SIXBIT code was commonly used for the first; for the second, the ASCII code (for Latin characters) was most popular, although IBM's EBCDIC also saw extensive use.
With the growth of computer use world-wide, along with per-language encodings, eventually the local ones were all replaced with Unicode, which contains most written symbols; in it, they are specified by variable-length codings (with the most common ones, such as the Latin characters of ASCII, still using only one byte).