From Teflpedia

A cleaner (/kli:nə/) is a professional who cleans places, particularly classrooms and teacher offices.

Cleaners tend not to be particularly well-paid, and often don't speak English, even in English-speaking countries where often they are immigrants. Making an effort with cleaners socially and keeping on their good side is definitely a good idea, as despite their lowly-paid status they are still your colleagues and especially if you work with children, you never know when you will need them to clear up something that's either a huge mess, disgusting or both.