Wikipedia
An ubosot ( `ubōsot ), phra ubosot (; phra `ubōsot ; Pronunciation) or, for short, bot (; bōt ; Pronunciation) is a building in a Buddhist wat. It is the holiest prayer room, also called the "ordination hall" as it is where ordinations take place.
The term ubosot, shortened to bot in Thai colloquial speech, is derived from the Pali term uposathagara, which refers to a hall used for rituals on the uposatha days -- the Buddhist Sabbath, which falls four times a month on the full moon, new moon, and eighth day after each.
An ubosot stands within a boundary formed by eight boundary stones which separate the sacred from the profane, and thus differs from a wihan (วิหาร). The sema stones actually stand above and mark the luk nimit , stone spheres buried at the cardinal points of the compass delineating the sacred area. A ninth stone sphere, usually bigger, is buried below the main Buddha image of the ubosot. Both ubosots and viharns typically house Buddha images. The entrance side of most ubosots face east. Across from the entrance door at the end of the interior is the ubosot's largest Buddha statue.