Jacket worn by head of the class (5)
I believe the answer is:
caste
'class' is the definition.
(type of social class)
'jacket worn by head of the' is the wordplay.
'jacket' becomes 'case' (I've seen this before).
'worn by' is an insertion indicator (outside letters are worn by those on the inside).
'head of' suggests taking the first letters.
The first letter of 'the' is 't'.
'case' going around 't' is 'CASTE'.
(Other definitions for caste that I've seen before include "Social system" , "Social order" , "Hindu social rank" , "Hereditary social class among Hindus" , "Hereditary class (in India)" .)