\
The backslash is a metacharacter that is used in regular expressions. It suppresses the special meaning of a metacharacter.
Example 1
/a\-b/ will match the string "a-b". The \ suppresses the special meaning of the range metacharacter -.
Example 2
/Account No\./ will match the string "Account No.". The \ suppresses the special meaning of the dot ( . ) metacharacter.