It is important in some contexts to make the distinction that a character is a unit of information, and does not imply any particular physical appearance. For example, the Hebrew letter "Aleph" is often used by mathematicians to denote certain kinds of infinity, but also of course in ordinary Hebrew text. In Unicode, for example, these two uses are different characters and are signified by two different codes, though they may look identical. Conversely, the Chinese ideogram for "water" may have a slightly different appearance in Japanese texts than it does in Chinese texts, and local typefaces may reflect this. But they nonetheless represent the same information, are considered the same character, and share the same Unicode value. The term glyph is used to describe a particular physical appearance of a symbol.
Computers and communication equipment represent characters using a character encoding that matches each character with an integer that can be stored and manipulated. The most common such encoding is ASCII, though the more versatile Unicode is quickly becoming popular.