a string or C string with the value ""
a string with a length of zero-- but it is a known value
A character string that contains no characters.
A string with no characters in it. It is represented explicitly in awk programs by placing two double-quote characters next to each other (""). It can appear in input data by having two successive occurrences of the field separator appear next to each other.
An empty character (""). A character that is not yet assigned a character string code.