A metacharacter is a character that has a special meaning to a computer program, such as a shell interpreter or a regular expression (regex) engine.
In POSIX extended regular expressions, there are 14 metacharacters that must be escaped — preceded by a backslash (\) — in order to drop their special meaning and be treated literally inside an expression: opening and closing square brackets ([ and ]); backslash (\); caret (^); dollar sign ($); period/full stop/dot (.
is escaped, it will lose its meaning as a metacharacter and will be interpreted literally as ".
The usual way to escape a character in a regex and elsewhere is by prefixing it with a backslash ("\").
Other environments may employ different methods, like MS-DOS/Windows Command Prompt, where a caret ("^") is used instead.