A fraction low? (6)
I believe the answer is:
vulgar
'low?' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for vulgar that I've seen before include "In bad taste" , "Coarse, lacking refinement" , "Rude and coarse" , "Improper - fractions may be so described" , "Lacking refinement, culture or taste" .)