The term hobby has several interconnected meanings:
In the Middle Ages, falconry was a very popular pastime (what today might be called a hobby), and of all the different birds used for it, the Hobby was perhaps the most popular. It is said that the modern use of hobby to indicate a pastime followed from this.
An alternative explanation is that the usage grew from another recreational animal called hobby: which was a type of small ambling or pacing horse. A '\'hobby-horse was a wooden or wickerwork toy made to be ridden just like the real hobby. From this came the expression "to ride one's hobby-horse", meaning "to follow a favourite pastime", and in turn, hobby'' in the modern sense of recreation.
Hobbies are practiced for interest and enjoyment, rather than as paid work. Examples include collecting, making, tinkering, sports and adult education. Engaging in a hobby can lead to acquiring substantial skill, knowledge, and experience. However, personal fulfillment is the aim.
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 a professional.
An important determinant of what is considered a hobby, as distinct from a profession (beyond the lack of remuneration), 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.
Astronomy is an interesting hobby in that the amateurs often make meaningful contributions to the professionals. It is not entirely uncommon for an amateur astronomer to be the first to discover a celestial body or event.
In the UK, the pejorative noun anorak is often applied to people who obsessively pursue a particular hobby. It probably originated as a consequence of the clothing invariably worn by train spotters and followers of touring car motor racing.
While some hobbies strike most people as trivial and boring, the hobbyist has found something compelling and entertaining about them (see geek). 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 therapeutic side effects. In some cases, however, (for example in collecting) the line between a hobby and an obsession can become blurred. There is more than one documented case of violence over things as simple as coin collecting.