Khmer romanization refers to the representation of the Khmer (Cambodian) language using letters of the Latin (Roman) alphabet. Romanization of Khmer is usually applied to Khmer proper nouns such as names of people and geographical names as in a gazetteer.
Romanization Systems for Khmer
Transliteration, where one script is mapped onto another. As transliteration is a system based on the writing system, it may not always reflect colloquial pronunciations.
When using transcription, words would be romanized based on the pronunciation. However, pronunciation of Khmer can vary by speaker and region. Transcription of Khmer is often done by "amateurs" on Internet forums and chatrooms (i.e. ad hoc romanizations) and is often referred to as Khmenglish or Khmerlish. Sometimes, the International Phonetic Alphabet is used to transcript Khmer words based on their Khmer spellings or their pronunciations.
There are a small number of romanization systems for Khmer but it is not used in Cambodia:
Is the only official romanization for Khmer, used many times in Cambodia, and today some people still using it. Nowadays, this romanization is rare as it is hard to use.
There is 12 versions of "Teesam" romanizations, Teesam1 is based on Polish, Teesam7 is based on German. Teesam6 and Teesam12 got its own system.
Teesam1 is first used in 2003, in Khmer language lesson in Warsaw, Poland, and this system is popular in Poland.
Teesam2 is planned to use in "Cambodia Map 3000" in 2005, however it got canceled. Same to Teesam3, Teesam4 and Teesam5. They renewed the 1956 system and name it "Teesam6" for Cambodia Map 3000. With some changes.
Teesam7 is used in 2006, for the Khmer community in Berlin, Germany.
Teesam8 is used in 2009, based on English, for international people who are learning Khmer. First used in "Learn Khmer" video on YouTube. It got deleted now. Now it is used frequently.
Teesam9 is based on Vietnamese, used in Vietnamese websites in the internet, but firstly used in "Khmer Box", which is the plain box with a Khmer poetry written in romanization. This box is located in Hanoi since March 1, 2010.
Teesam10 is based on chinese pinyin and planned to use for learning Khmer in China. But it's never used.
Teesam11 and Teesam12 is currently under construction.
Khmer romanization using the system from United Nations Group of Experts on Geographical Names can be seen in most recent maps with Cambodian geographical names and in the newer gazetteers.
ALA-LC Romanization Tables
From the American Library Association and Library of Congress -- the system for romanizing Khmer uses the original Indic values of Khmer letter for romanization which are totally different from their modern values. The advantage of this system is that it is possible for etmylogical reconstruction of Sanskrit and Pali loanwords whose pronunciation may be totally different in modern Khmer, (e.g. Kampuchea and Kambuja).
Service Géographique Khmer
From the Khmer Geographical Service based in Cambodia.
the United States Board on Geographic Names & Permanent Committee on Geographical Names for British Official Use
Various attempts have been made to modify the International Phonetic Alphabet IPA to transcribe Khmer (and not always phonetically!). The widespread use of J.M. Filippi's 2004 Textbook Khmer au quotidien, a.k.a., Everyday Khmer (Funan Editions: Phnom Penh) has resulted in a classroom pseudo-standard that follows IPA in its broad outlines (e.g., marking long vowels with the triangular colon), but also digresses from it for reasons the textbook leaves unexplained (e.g., perhaps just due to widespread familiarity with certain assumptions inherited from the aforementioned Pali etymological tradition, e.g., rendering "ch" sounds as Roman /c/).