Where an office is concerned, one may be in or out (4)

I believe the answer is:

tray

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But I can't explain it at all! Could you help me understand?

(Other definitions for tray that I've seen before include "Carrier (for eg, crockery, food)" , "Carrier for crockery etc" , "Flat board for carrying things" , "Shallow receptable for carrying something" , "Flat utensil for carrying meal" .)

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