Each of Cambodia's 23 provinces is divided into districts - as of 2010 there are 159 districts (ស្រុក, srok) and 9 districts in Phnom Penh (ខណ្ឌ, khan).
Each of the provinces has one capital district, e.g. for Siem Reap it's Srok Siem Reap.
The exceptions are Banteay Meanchey, Kandal, Mondulkiri, Oddar Meanchey, Preah Vihear Province and Rattanakiri, where the province and the capital district does not match together.
In Phnom Penh the districts are called khan (ខណ្ឌ), and their subdivisions sangkat (សង្កាត់) which are smaller in the other provinces.
The sangkat are further subdivided into phum (ភូមិ), which are usually translated as villages, though they do not necessarily cover one single settlement.
Additionally to these subdivisions, there are also cities and towns, which take over some of the responsibilities of the districts and communes on the area covered by the municipality. These all have an elected board and an elected mayor.
There are three different levels of municipalities (Khmer: ក្រុង):
krong (city): More than 50,000 citizens
krong (town): More than 10,000 citizens - or a provincial capital
In addition to the population numbers the municipalities need to have enough tax revenues for the administration to be able to execute the offices of administrations.
Towns and cities are into sangkat (quarters), which are equivalent to the villages (phum) of rural areas.
For areas which does not reach the mandatory conditions there exists another lower level of local administration. These usually cover a complete subdistrict (Khum), but may also cover more than one subdistrict or share a subdistrict with a municipality.
Kandal Province is informally included as part of Phnom Penh, as the urban sprawl of the capital already spread into these areas.
There are several definitions of regions in Cambodia.
Cambodia Town, Long Beach, California is sometimes jokingly referred to as "The 24th Province" of Cambodia, because the city has the second highest Cambodian population of any city outside of Cambodia (roughly 50,000) after Bangkok(??) (roughly 1,200,000).