Curriculum used is different from the national curriculum in the school's country of residence, students are mainly expatriate.
An international school is a school that promotes international education, in an international environment, either by adopting a curriculum such as that of the International Baccalaureate, US Common Core or IGCSE, or by following a national curriculum different from that of the school's country of residence.
This type of school is what most people visualise when they think of teaching abroad- a UK school with UK curriculum and British students taught by British teachers, it just happens that the school is not in the UK. Many decades ago, when international relocation was something few people did, this kind of school was the only type, but now they represent the smallest proportion of international schools available.
There are a number of international schools in China that are well established and well known. Having been some of the first international schools in the country, they often charge fees to parents that are at the top of the regional range and therefore offer very competitive employment packages to teachers. Anyone looking to work here would be required to have full teaching certification and a significant amount of experience working with the target curriculum.