Keep overlooking a messy area (3)

I believe the answer is:

sty

I'm a little stuck... Click here to teach me more about this clue!

'messy area' is the definition.
(I've seen this in another clue)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for sty that I've seen before include "Pig-pen and eye infection" , "Pig pen" , "Pigpen; swelling" , "Sore on eyelid" , "Porcine pen" .)

I've seen this clue in The Independent.

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