Question: What is considered “racking one’s tile”?

Answer: Racking occurs when a tile is fully placed on the sloped part of one’s rack. Tapping or merely touching your tile is not considered placing your tile on your rack. Although racking one’s tile is not mandatory, it is highly recommended because it closes the window of opportunity for another player to call the previously thrown tile.

Source: Mah Jongg Made Easy 2024,  pg. 17, #8