An adapter allows two pieces of electronic equipment to be used together, or an electronic device to take power from a supply source. The adapter is what allows the device to make use of electricity.
Ex: Does anyone in the room have an AC adapter that will fit my laptop? I have forgotten mine in my car which is parked across the street in a garage and I'd prefer not to get it until lunch.
Ex: Before Sue took her trip overseas, she carefully considered the type of adapters she would need in order to operate her electronic equipment in the various countries she would be visiting.
An adapter can also refer to a person who transposes, adapts, or makes changes* to music so it can be played by multiple instruments. If you adapt* a piece of music written for a piano for the guitar, you are making changes to the music so it can be played on a different instrument.
Ex: My cousin Ian is a concert pianist. In the off-season, however, he works as an adapter for various musicians across the country who desire to play certain pieces, but don't have the technical skill to adapt the musics themselves.
Ex: Before I say yes to playing this piece on the harp, I would like to make sure you have the right adapter who has worked with music for the harp before. Changing a piece like this can be very difficult.