The shape of a snowboard is categorized as directional, twin or directional twin.
Twin boards are completely symmetrical meaning that the nose and the tail are the same shape and flex allowing the rider to ride the board regular or "switch", where their other foot is now forward.
Directional Twin snowboards tend to be the most popular shape. The nose and tail are not completely identical, but they are very similar and vary only slightly in flex and shape. Directional twin boards are made to be ridden in one direction the majority of the time but still ride well switch.
Directional boards have a specific nose and tail with a different shape and flex. The nose is generally longer and the tail is shorter and sometimes stubbier. The board is designed to be ridden in one direction.