Cambodian French refers to the use of French language in Cambodia. French is a language that comes from a country called France and it is spoken by people who are from that country. A long time ago in the 1800s, France went to Cambodia and made it a part of their own country. This means that the people who lived in Cambodia had to learn how to speak French because that was the language that the people in charge spoke. French became the second official language of Cambodia, alongside Khmer, which is the native language. This means that even though Khmer is the main language spoken in Cambodia, people also use French to communicate with each other.
When France gave Cambodia their independence in 1953, the use of French decreased but it still remained an important language in business, education, and government. Today, some Cambodian people learn French in school or from their parents, and others use it as a way to communicate with people from other countries.
So, basically, Cambodian French is just the use of French language in Cambodia that started a long time ago when France made Cambodia a part of their country. Even though Cambodia is its own country now, some people still speak French there.