Cambodia is divided into 25 provinces (Khmer: ខេត្ត, khaet, singular and plural). The capital Phnom Penh is not province but a special administrative area and is included as the 25th province since it is administered at the same level as the other 24 provinces.
Phnom Penh has both the highest population and the highest population density, but is the second smallest in land area. The largest province by area is Mondulkiri and the smallest is Kep which is also the least populated province. Mondulkiri has the lowest population density despite being the largest province.
Each province is administered by a governor, who is appointed by the Ministry of Interior.
Cambodia is subdivided into 163 districts (srok, ស្រុក). The 12 districts of Phnom Penh are called khan (ខណ្ឌ), but even in official documents they are sometimes misidentified as srok. The number of districts in each province varies, from two in the smallest provinces to 14 in Battambang, Prey Veng, and Siem Reap. Further subdivision levels are khum (ឃុំ)(subdistricts), sangkat (សង្កាត់)(quarters) and finally, phum (ភូមិ) (villages). In Phnom Penh there are no khum.
More information on the Wikipedia page