A string that literally appears in your program's source code text file. (see string handling in C).

If you are programming in C, then a string literal might look like the following in your source code:

.
.
.
j = j +1;
if (j > 17) {
    printf("This is a string literal");
}
blah1();
blah2();
.
.
.

The text "This is a string literal" above is a string literal.