Adapter may refer to any of the following:
1. In general, an adapter refers to any additional circuitry built onto the computer or that comes in the form of an add-on that gives the computer additional functionality or compatibility. For example, a video adapter gives the computer the capability to have video displayed on a computer monitor. Although most video adapters come in the form of an expansion card, they can also be onboard. The picture is a PS/2 to USB adapter and another example of an adapter. In this example, the adapter allows a PS/2 mouse to work with a USB port.
Both "adapter" and "adaptor" are correct spellings when referring to a device. However, Computer Hope always uses "adapter" when referring to a device such as a video adapter.
3. Adapter is also a name of a free video and audio converter for Apple and PC's that convert from one file format into another.