A type of extension cord that has two set of duplex Edison (NEMA 5-15) outlets (a total of 4 total outlets, hence the name "quad" box). Typically all outlets are on the same circuit. Also known as a "1900 box," as 1900 is/was the model number by one manufacturer of a two-gang box. Today, the pre-punched knock-outs make such a box unsuitable for anything other than an in-wall installation.
A quad box designed specifically for the construction industry, with an integral GFCI: