Pretty girls, perhaps, but they go to the wall (3-3)
I believe the answer is:
pin-ups
'pretty girls' is the definition.
The answer and definition can be both people as well as being plural nouns.
Perhaps you can see an association between them that I can't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for pin-ups that I've seen before include "Posters of stars" , "They may be very pretty" , "Cover girls" .)