A small transducer, housed in a maple disk, sticks to the surface of your guitar near the bridge with a special adhesive. The adhesive allows it to be removed and re-stuck many times without affecting the finish of your guitar.
It's not difficult to make a vintage single-coil pickup that's clean and bright, but not so easy if you also want the high strings to sound sweet above the 12th fret. The True Velvet was designed to make this happen by tuning the coil to a frequency range that's bright but not thin. DiMarzio combined this with a magnet stagger specifically designed to enhance string balance, which produces great clarity, even with full chords.