The traditional Mah Jong tile set consists of 136 tiles. The tiles are divided into two main groups: Suits and Honors.
There are three suits: Bamboos, Characters and Dots. Each suit consists of 36 tiles: four 1s, four 2s, and so on up to 9. Total of suit tiles is thus 108.
Suit tiles from 2 to 8 are called Simples (or Minor tiles, as opposed to Terminals and Honors, which are sometimes called Major tiles), 1s and 9s are called Terminals. Sets composed of Terminals pay generally more than sets composed of Simples.
Honors consist of Dragons and Winds. There are three Dragons four of each: Green Dragon, Red Dragon and White Dragon, and four Winds, four of each: East, South, West and North. Total of honor tiles is thus 28.
Letters on the Dragon tiles are based on the Chinese terms fa (signifying "flourishing manifestation", and symbolizing Earth), chun (meaning "centre", and symbolizing Man), and pai pan (meaning "white plank", "white tile").
When the game was introduced in the USA, numbers and letters were added on the tiles to make them easier to recognize. You can hide the tile identifiers, if you want to, by clearing the check mark from the menu command Show Tile Ids on the Options menu (not available when customized tile bitmaps are used).
Related topics:
Goal of the game
Extra tiles
Sets
Deal
Regular pace of the game
Declaring a melded Kong
Declaring a concealed Kong
Robbing a Kong
Declaring Ready
Going out
Deal ends in a Draw
Faulty declaration of Out