A variable length string is usually ended with a null (\0) character. Most often referenced by a char pointer, since they will royally screw up a typical data structure (as everything after the string will be at an indeterminate position), they are what all those
str functions manipulate.
The old writeup (preserved for posterior
(sic)):
A
string of
variable length. This should be
obvious.
A variable length string is also a self-explaining term.