answer
It's running 6 or more decks in a CSM, and pulling out a two deck slug, and hand dealing that slug. When most of those cards have been dealt, they are returned to the CSM, and shuffled back into the whole mix. Another slug is then pulled, and the sequence starts again.
Essentially, it's the same as less than 2D penetration. Sometimes, the casinos call it 6D hand held.
Stay away from it.