string/1

Availability:built-in

string(@Term)

True if Term is bound to a string. Note that string here refers to the built-in atomic type string as described in section 5.2. Starting with version 7, the syntax for a string object is text between double quotes, such as "hello".^{62In
traditional Prolog systems, double quoted text is often mapped to a list
of character codes.} See also the Prolog flag double_quotes.