Crossword Genius

Pretty girls, perhaps, but they go to the wall (3-3)

Ross

I believe the answer is:

pin-ups

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'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" .)

I've seen this clue in the Evening Standard.
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