Music Production
Phantom power (+48V)
A 48-volt supply sent down an XLR cable from the interface to power a condenser mic.
A standard 48-volt supply sent down a balanced XLR mic cable to power the electronics inside a condenser microphone. It's switchable on most audio-interface and mixer preamps, usually labelled '+48V' or 'phantom'. Condenser mics generally require it to work at all; standard dynamic microphones don't need it and are designed to be unharmed by it, so leaving it on for a dynamic mic is normally fine.
Concrete example
plug in a studio condenser, hear nothing, and the usual fix is that +48V isn't switched on.
What it means when you're buying
make sure your interface supplies phantom power on the inputs you'll use for condenser mics — most do, but very basic or instrument-only inputs may not — and switch it off before unplugging mics to avoid pops.