From the Wikipedia page 
The Japanese tea ceremony, also called the Way of Tea, is a Japanese cultural activity involving the ceremonial preparation and presentation of matcha, powdered green tea. In Japanese, it is called 茶の湯 (chanoyu) or 茶道 (chadō, sadō). The manner in which it is performed, or the art of its performance, is called お手前; お点前 (otemae). Zen Buddhism was a primary influence in the development of the tea ceremony. Much less commonly, it uses leaf tea, primarily sencha; see sencha tea ceremony.
Tea gatherings are classified as 茶会 (chakai) or 茶事 (chaji). A chakai is a relatively simple course of hospitality that includes confections, (thin tea/薄茶/usucha), and perhaps a light meal. A chaji is a much more formal gathering, usually including a full-course kaiseki]] meal followed by confections, nihongo (thick tea/濃茶/koicha), and thin tea. A chaji can last up to four hours.