String literal is a sequence of arbitrary characters enclosed either in single quotes or in double quotes. Both these forms are equivalent.
If the single quote is a part of a string literal enclosed in single quotes, it must be coded twice. Analogously, if the double quote is a part of string literal enclosed in double quotes, it must be coded twice.
'This is a string' "This is another string" '1 + 2 = 3' 'That''s all' "She said: ""No"""
String literals are used to represent symbolic quantities.