A profession is a job that involves specialised knowledge and training and which has a stated or implied code of conduct. The word profession comes from "profess", which is to take a vow. It is considered that a professional person has a greater standard of ethics than that expected in a more common job.
Doctors, lawyers, and teachers are all considered professionals.
The term may be used to indicate a person who is highly skilled at a specific job, like a plumber or carpet cleaner.