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wall wart: n.

A small power-supply brick with integral male plug, designed to plug directly into a wall outlet; called a ‘wart’ because when installed on a power strip it tends to block up at least one more socket than it uses. These are frequently associated with modems and other small electronic devices which would become unacceptably bulky or hot if they had power supplies on board (there are other reasons as well having to do with the cost of UL certification).