A rule which is flexible (4,7)
I believe the answer is:
tape measure
'a rule' is the definition.
(I know that tape measure is a type of rule)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tape measure that I've seen before include "one might have a few feet on it" , "Flexible strip showing lengths" , "Device for finding length of cloth etc" , "band covering the distance?" , "Tailors may use one" .)