It's a cheap USB 2.0 'thumb' drive. We have all our music, radio plays and spanish lessons on it.
It plugs into the dash on our tow vehicle, and the radio recognizes what it is, and knows what's on it, down to artist, album and track.
No more compilation CDs of mp3s, no more shuffling around trying to find *that* song. It's all there, on one little thumb drive.
We've used it a lot this trip, when we've been out of cellular data and radio range.
Love it