It's about mothers concealing their aspirations (6)
I believe the answer is:
dreams
'aspirations' is the definition.
('dream' can be a synonym of 'aspiration')
'it's about mothers concealing' is the wordplay.
'it's about' becomes 're' ('re' means regarding or about).
'mothers' becomes 'dams' (dam can mean the mother of an animal).
'concealing' means one lot of letters goes inside another.
're' going within 'dams' is 'DREAMS'.
'their' is the link.
(Other definitions for dreams that I've seen before include "Fantasy ambitions" , "Imaginings" , "Reveries or cherished aspirations" , "Thoughts and visions during sleep" , "Fantasies; fantasises" .)