Strictly speaking a wat is a Buddhist sacred precinct with a vihara (quarters for bhikkhus), a temple, an edifice housing a large image of Buddha and a structure for lessons. A site without a minimum of three resident bhikkhus cannot correctly be described as a wat although the term is frequently used more loosely, even for ruins of ancient temples. As a transitive or intransitive verb, wat means to measure, to take measurements; compare templum, from which temple derives, having the same root as template.
In everyday language in Thailand, a wat is any place of worship except a mosque (Thai สุเหร่าsurao or มัสยิดmasjid; a mosque may also be described as โบสถ์ของอิสลาม - bodkhong Isalam, literally "Islamchurch"). Thus a wat cheen is a Chinese temple (either Buddhist or Taoist), wat khaek is a Hindu temple and wat krit or wat farang is a Christian church, though Thai โบสถ์ (โบสถ์bodkhong) may be used descriptively as with mosques.
In Cambodia, a wat is used to refer to all kinds of places of worship. Technically, wat generally refers to a Buddhist place of worship, but the technical term is វត្តពុទ្ធសាសនាvott poutthosaeasanea. A Christian church can be referred as វិហារយេស៊ូvihear Yesaou or "Jesus vihear". Angkor Watអង្គរវត្ត means "city of temples".
According to Thai law, the Thai Buddhist temples are categorised into two types:
The facade to the Phra Viharn Luang (meeting hall) at Wat Suthat, one of the most important Buddhist temples in Bangkok, Thailand
Wat (Thai: วัด; RTGS: Wat) are the temples having been endorsed by the State and having been granted the Wisungkhamasima (วิสุงคามสีมา), or land for establishment of central hall, by the King. These temples are divided into:
Royal temples (พระอารามหลวง; Phra Aram Luang), established or patronised by the King or his family members.
Private temples (วัดราษฎร์; Wat Rat), established by the private citizens. Despite the term "private", the private temples are opened to the public and are the sites of public religious activities also.
Samnak Song (Thai: สำนักสงฆ์; RTGS: Samnak Song) are the temples without state endorsement and the Wisungkhamasima.
A typical Buddhist wat consists of the following buildings:
chaidei or chedi (Khmer ចេតិយ), (Thai เจดีย์) (from Sanskrit: chaitya, temple) - usually conical or bell-shaped buildings, often containing relics of Buddha
vihear (Khmer វិហារ),wihan (Thai วิหาร) from Sanskrit: vihara) - a meeting and prayer room
mondop (Thai มณฑป) (from Sanskrit: Mandapa) - a usually open, square building with four arches and a pyramidal roof, used to worship religious texts or objects
sala (Khmer សាលា), (Thai ศาลา) (from Sanskrit: Shala - School, from an earlier meaning of shelter) - a pavilion for relaxation or miscellaneous activities
botโบสถ์ or ubosothอุโบสถ์ (from Paliuposatha) - the holiest prayer room, also called the "ordination hall" as it is where new monks take their vows. Architecturally it is similar to the vihara; the main differences are the eight cornerstones placed around the bot to ward off evil. The bot is usually more decorated than the viharn.