The "Drop 2" chord voicing technique is a common arranging/composing/piano trick. It's a great way to voice a chord for a horn section, or if you're a piano player, it's a slick way of creating strong 4- or 5-note voicings.
1) Start with a 4-note chord that exists all within an octave. (This may be a chord in root position, but may also be a different inversion of a chord, or some other type of cluster.)
2) Identify the second highest note (the "2" of "Drop 2").
3) Move this note down an octave.
Here's a step-by-step video showing the process: