Box

The term of box was applied to many types of usually-rectangular containers. Not least among them where the police boxes whose form was borrowed by the Doctor's TARDIS after her visit to 1963 London, prompting the Doctor to define themselves as "a madman with a box" (or variations thereof) on many occasions.

The TARDIS as a box
Following a stopover in 1963 London, the Doctor's TARDIS was stuck with the exterior shape of a telephone box, specifically a police box, due to a malfunction in its chameleon circuit. (TV: "The Cave of Skulls") As the First Doctor explained to Ian Chesterton and Barbara Wright, the box was an entrance chamber to a fourth dimension, leading directly into the control room. (COMIC: The Secrets of the Tardis)

The Doctor would continue to refer to his TARDIS as a "box" all throughout their lives; the Eleventh Doctor called himself "a madman with a box" (TV: The Eleventh Hour) and, while believing he was dying, looked back on his story as that of "a daft old man who stole a magic box and ran away". (TV: The Big Bang) He referred to the TARDIS's physical shell as "the box" when the heart of the TARDIS wrenched back control of said shell from House, declaring that "now she [was] back in the box again". (TV: The Doctor's Wife) His next regeneration, at a turning point in understanding himself, proclaimed himself "an idiot! With a box, and a screwdriver!". (TV: Death in Heaven)

Other boxes
Pandora's box was a legendary item to which the Pandorica bore a resemblance. Before he was made aware of its true nature by the Dalek members of the Pandorica Alliance, the Eleventh Doctor also derisively called the Pandorica "a box". (TV: The Pandorica Opens)

An advanced, interactive computer who served as Liz Shaw's companion shortly before her retirement from the Preternatural Research Bureau also went by the name of Box, as, indeed, she resembled one. (HOMEVID: When to Die)

Despite forming an alliance with the Daleks, privately grumbled them off as "stupid tin boxes", in a contemptuous reference to their casings. (TV: Frontier in Space)