QUOTNAME Function in SQL Server

QUOTNAME()
Returns a Unicode string with the delimiters added to make the input string a valid Microsoft SQL Server delimited identifier.

Syntax
QUOTENAME ( 'character_string' [ , 'quote_character' ] )   Arguments
character_string '

Is a string of Unicode character data.

Character_string is sysname and is limited to 128 characters. 

Inputs greater than 128 characters return NULL.

' quote_character '
Is a one-character string to use as the delimiter. 

Can be a single quotation mark ( ' ), a left or right bracket ( [ ] ), or a double quotation mark ( " ). 

If quote_character is not specified, brackets are used.

Return Types: nvarchar(258)