A witch doctor is a person — almost always described as a man — believed to have magic powers, who is asked to cure sick people, take curses off them, or tell the future. English speakers use the word mainly about traditional healers in parts of Africa, and sometimes about similar figures elsewhere.

Here is the important part, and it is the part dictionaries often say too quietly: this is an outsider's word. It came from British colonial times, and it carries the idea that what the person does is superstition, not real medicine or real religion. People who actually visit such healers do not call them witch doctors; they have their own words. Careful writers today say 'traditional healer' or use the local name (in South Africa, for example, 'sangoma'). So you can meet this word in older books and films with no problem, but if you use it yourself about a real living person, you may sound rude, or as if you think their culture is silly.

There is a second, jokey use in normal speech: people call a doctor a witch doctor when they think the treatment is nonsense. 'He went to some witch doctor who told him to drink vinegar.' That is a complaint about the doctor, not about Africa.

Note also that 'witch doctor' does not mean a doctor who IS a witch, and does not mean someone who treats witches. The two words together name one job: a magic healer.