Henry and Norm snatch back chart (3,5)
I believe the answer is:
bar graph
'chart' is the definition.
(bar graph is a kind of chart)
'henry and norm snatch back' is the wordplay.
'henry' becomes 'H' (symbol for the unit of electrical inductance).
'and' is a charade indicator (letters next to each other).
'norm' becomes 'par' (I've seen this in another clue).
'snatch' becomes 'grab' (synonyms).
'back' says the letters should be written backwards.
'par'+'grab'='pargrab'
'pargrab' reversed gives 'bargrap'.
'h' after 'bargrap' is 'BAR GRAPH'.
(Other definitions for bar graph that I've seen before include "Lines of varied lengths" , "Grab harp (anag.)" , "Chart with blocks, their lengths proportional to quantities" , "Diagrammatic representation of comparative amounts" .)