Whilst a folding card table might be designed in any shape (square, circular, oval, hexagonal or octagonal) traditionally they're square shaped. This shape is very convenient for games where there is a fixed at quantity of players. For instance, there are always four players for the games of auction bridge or whist. Similarly, there will always be two players in a game of bezique or piquet. Having a square table permits the different pairs (or players in the case of two-handed games) to sit facing each other in a way that there's absolutely no way of another player's cards being seen.
A typical square folding card table would be three feet square as this size allows a decent playing area whilst at the same time maintaining your folded table sufficiently small to be easily stored when not in use. It will be designed so that only a minimum of floor space is going to be adopted when the table isn't being used.
A round or oval shaped table would be better for those card games which are played without a fixed quantity of players; rummy and canasta have been in this category. Round tables are far more common than their oval counterparts if perhaps because it is a simpler matter to design and construct a round folding card table than an oval one.
Other shapes (hexagonal, octagonal, etc.) are noticed very rarely.
Whatever the shape, the covering from the playing part of the table will have to be non reflective (so they won't reveal cards during the dealing process), need to be non slip (to help keep cards from skidding around whilst being dealt) and want to permit the simple obtaining of dealt cards. In practice, these properties are supplied by fixing a baize covering to the surface of the table. This covering will usually be colored green, although blue baize is often used. The greater sophisticated tables won't have their tops completely covered in baize. A place of wood will be left uncovered for each player to use for drinks, with no problem of staining the baize, which, being fixed to the top of the table, could be difficult to clean.