A zendo is a meditation hall, the room in a Zen temple or center where zazen is practiced. In a traditional monastery, monks may also eat and sleep in the same hall.
The space is deliberately plain. Cushions are set in rows along the walls, there is usually an altar, and the hall is kept quiet and orderly so that nothing pulls at the attention.
Entering a zendo has its own etiquette, such as bowing at the door and to one's seat. The forms differ between schools, and newcomers are normally shown what to do.