What does tarot card size mean?
Tarot is played with 78 cards and at the beginning of the game a player's hand is quite big (18 cards for a 4-player game ; 15 for a 5-player game and 24 for a 3-player game). With an ordinary format (Poker or Bridge), it would be difficult to hold them, so Tarot cards are longer and narrower.
The measurements I found are 60mmx120mm.
More info (in French) on the wikipedia page