Shark is a strong gambler. This term often means people who understate their knowledge and gambling abilities in order to get the best of lack of experience of other people.
Shoe is a special device for the physical casino. The pack of shuffled cards is inserted into the shoe, and then the cards will be handled from it.
Showdown takes place at the end of the card game for comparison of the combinations of the gamblers. This term is more frequently used in poker.