A profession is a job at which someone works and for which they have had training. It is what they do to get money or a living. People often study for years to do their job. Medieval Europe recognized three professions: divinity, medicine, and law. These were called "learned professions". In modern times other occupations such as teacher or engineer are often called "learned".
Sometimes "profession" only means learned professions, but the word may also be used for other jobs. Someone who works in a profession is called a professional. Sometimes this is in contrast to amateur which means someone who does similar things but is not paid.