A tile is "free" when:
Two tiles are identical if they look exactly the same. Except for the Flowers and Seasons tiles. They are non-identical matching tiles and belong to the same type. All the Flowers and Seasons tiles match one another inside their group type.
Each tile appears four times in a standard solitaire mahjongg game. Again an exception for the Flowers and Seasons tiles who appear only once each during a game.
The 9 circle tiles - their numerical values are represented by the number of circles shown on the tiles. There are four tiles of every circle tile (36 tiles total).
The 9 bamboo tiles - their numerical values are represented by the number of bamboo sticks shown on the tiles. There are four tiles of every Bamboo (36 tiles total).
The 9 characters tiles - their numerical values are represented by the red and black Chinese numeric symbols. There are four tiles of every Character (36 tiles total).
Please note, all tiles in this game implementation have additional Arabic numbers to help players to identify matching tiles.
The four seasons tiles appear once each in a game (4 tiles total). Spring, Summer, Autumn and Winter. Printed above is the the corresponding abbreviations for the seasons. In mahjong solitaire any season will match another season.
The four wind tiles also appear once each in a game (4 tiles total). East, South, West and North. Shown on every tile is the Chinese symbol for the according wind. The first letter of the wind is printed using Latin characters. There are four tiles of every wind (16 tiles total).
The dragons tiles. Green Dragon, White Dragon and Red dragon. There are four tiles of every dragon (12 tiles total).