What are hobbies for some people are professions for others: a computer game tester may enjoy cooking as a hobby, while a professional chef might enjoy playing (and helping to debug) computer games. Generally speaking, the person who does something for fun, not remuneration, is called an amateur (or hobbyist), as distinct from professional.
An important determinant of what is considered a hobby, as distinct from a profession, is probably how easy it is to make a living at the activity. Almost no one can make a living at stamp collecting, but many people find it enjoyable; so it is commonly regarded as a hobby.
While some hobbies strike most people as trivial and boring, the hobbyist has found something compelling and entertaining about them. Much early scientific research was, in effect, a hobby of the wealthy; in our own time, Linux began as a student's hobby.
Pursuit of a hobby often has calming or helpful thereputic side effects.
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