Learn more about Amateurconnotations. In the first, more widely used manner, it means someone performing some task without pay, in contrast to a "professional" who is paid for the same task. In this sense, labeling someone an "amateur" can have a negative connotation. For example, amateur athletes in sports such as basketball or football would not be regarded as having ability on par with professional athletes in those sports.
Where this can be interesting is in the case of the Olympic Games. Until the 1970s, most Olympic events required that the athletes be amateurs. To receive pay to perform the sport disqualified an athlete from an event, as in the case of Jim Thorpe. Such regulations have now been relaxed for all Olympic sports, with the exception of boxing.
Also in the areas of computer programming and open source, and astronomy and ornithology, many amateurs make very meaningful contributions equivalent to or exceeding those of the professionals. To many, description as an amateur is losing its negative meaning, and actually carries a badge of honor.
The other, perhaps somewhat obsolescent usage, stems from the French form of the Latin root of the word meaning a "lover of" (see amateurism.) In this sense, retaining its French inflexion ("am-a-tEUR"), an amateur is motivated by a love or passion for the activity. In the 17th and 18th centuries virtuoso had similar connotations of passionate involvement.
Another thriving example of such work is amateur dramatics - whether plays or musical theater, often performed to high standards (but lacking the budgets of the professional West End theatre/Broadway theatre versions) and with an intense passion for the scene.
It has been suggested that the crude, all-or-nothing categories of professional or amateur should be reconsidered. A historical shift is occurring with the rise of pro-ams, a new category of people who pursue amateur activities to professional standards.