A box fold is simply referring to the bending of the metal in the panel box. The sheet metal is folded into a box-like shape as opposed to a rounded shape. In this case, it gives a place for wedges to hold the light holder in place.

References
Perhaps the most impressive thing about the activepanel was the quality of the packaging; it took me a good five minutes to fight my way in to the inner box constaining the panel, which sat so snugly in its cardboard home I thought I would never get it out.
The activepanel is mounted in a folded steel box held together with cruciform screws and the general fit of the components was excellent.
http://www.flightsim.com/cgi/kds/main/review/itra/itra.htm

Generator control panel suitable for mounting on or over the alternator terminal box... The circuit breaker is fitted within a separate enclosure for mounting onto the side of the alternator terminal box complete with cables for connection to the alternator terminals. This degregates the load from the control wiring and allows more space for optional extras.
Manufactured from folded and welded zinc coated steel. IP42 and finished in black polyester powder coating.
http://www.genpart.co.uk/products/pdf_datasheet/digital_over...

Here you see the panel almost done and ready for bonding into a chassis. In the background others are working on jigs that will hold the folded panel as it is glued. On hand was a visitor from Lockheed to lend advice.
Here you see a carbon panel used in the cut and fold method for making a chassis. Lines of the top skin are routed allowing the panel to be carefully folded into a box-like structure.
http://www.opencortex.org/cn00000214

châssis en tôle pliée E24 ou inox 304L
http://www.electra.fr/pieces_fiches/47_f6.pdf#search='b...
PRESENTATION DU METIER DE CHAUDRONNERIE
aux Olympiades internationales
Le candidat doit réaliser, seul, les tâches suivates :
Techniques de reproduction des formes développées de l’épure sur la tôle
Procédés de découpage
Procédés de formage
- pliage
Excercice nº 1 : Sujet : « Boîte pliée »
http://www.formation-info.org/Olympiades/Fichiers_pdf/Guide ...