Indexing
Indexing is a cheater's technique to mark cards with a fingernail or a device, so that the cards can be recognized later. It is a form of marking cards.
The simple explanation
A cheater makes tiny marks on the edges of cards. He can later tell which card it is, even when it is face down.
A closer look
Indexing is a serious form of cheating. Honest rooms change decks regularly and inspect them. If you notice odd marks, bent corners or scratches, tell the floor and ask for a new deck. Do not try to use marked cards yourself, since that is cheating too.
A practical example
A floorman finds fine nail marks on the edges of several aces and changes the deck.
Full explanation
Indexing is a cheater’s technique to mark cards with a fingernail or a device, so that the cards can be recognized later. It is a form of marking cards.
Indexing is marking cards.
It is done with a fingernail or a device.
It is cheating.
Call the floor if you see marks.