An adapter or adaptor is a device used to match the physical or electrical characteristics of two different things so that a connection may be made between them.

An adapter may be very simple, connecting one kind of plug to another kind of socket, but not changing what passes through. One example would be a garden hose, which normally has threads that screw on, but can be attached to an adapter which allows it to snap easily on and off of faucets, other hoses, or attachments. Likewise, a serial port may require an adapter to connect between the old DB-25 type and the later DE-9 type, which have 25 and 9 pins (respectively) but only 9 wires each.

Other adapters may include a device that changes what is passing through, such as a transformer that adapts household electrical current from high voltage (100 to 240 volts) to low voltage (3 to 24 volts) suitable for consumer electronics.

Computing

Adapters in computing are even more complex, requiring digital translation (or even digital signal processing in the case of converters).

Universal Serial Bus (USB) adapters are available for printers, and for keyboards and mice, among others.

An Ethernet adapter is the hardware required to attach to an Ethernet network. It normally resides on an expansion board, but sometimes it is built into the motherboard.

See also: port (computing), scan converter