To remove the special meaning
from some character
typed into a computer system, causing the text to be interpreted literally
For example, at a Unix shell prompt, to refer to a file with whitespace in its name requires enclosing the filename in quotes or otherwise quoting the space in the name, to keep it from being interpreted as two separate filename arguments.
When writing a regular expression
(perhaps a search pattern for a utility like grep),
if the string to be matched happens to contain a regexp metacharacter such as a bracket or asterisk,
it must be quoted with a backslash to remove its special meaning.