Shuffle tracking is a rather new casino technique. It's not too popular among amateur players because it relies on one's tough observation and memory skills. Needless to say that shuffle tracking does not work in online casinos because casino software tends to reshuffle cards after each game round in even and fair fashion. Also known as "cluster tracking", shuffle tracking analyses the methods the dealer uses to shuffle the cards and exploits shuffling flaws to make assertions about "clusters" of card likely appearing in this or that part of the deck after the shuffle.
Obviously, shuffle tracking is useless in online blackjack, because online blackjack dealers are computers that shuffle the decks in even and fair fashion. There are however some interesting theories that combine blackjack card counting, shuffle tracking, betting management systems and basic strategy to produce powerful and useful blackjack strategies.