Metacharacters are characters that have special meaning in certain contexts. For example, the characters '*' and '?' have certain special significance in building regular expressions or in the identification of groups of files to the Shell.
Special characters that let you specify a wildcarded name expression. For example, the asterisk (*) matches zero or more characters.
Literal characters interpreted by a parser.
Characters that have a role is specifying HTML syntax, such as "", "", or "&".
Characters that have special meaning instead of a literal meaning.
the section called “Regular expression metacharacters
Characters used within a regexp that do not stand for themselves. Instead, they denote regular expression operations, such as repetition, grouping, or alternation.