The slang term "one trick pony" is used to refer to something that can only be used for one very specific application, or a person who can only do one thing well. A chef who can only produce one really good dish, for example, might be described as a one trick pony. The phrase is generally used in a disparaging way, since it suggests a lack of flexibility and an inability to work outside very specific parameters.
The term probably originates in early 19th century in America from small circuses called "dog and pony shows." These circuses had a limited number of animals and performers, and often the shows were simple or lackluster. A horse that performed just one trick probably wasn't considered very impressive.
The exact origin of the phrase is not known, but it was in popular use at least as far back as 1905; there is a mention of a traveling circus featuring a one trick pony in a reunion announcement for the Oregon Pioneer Association. The term fell out of use, so much so that some people think the phrase originated with a 1980 movie and recording created by musician Paul Simon, both titled One Trick Pony.
Some industries are particularly known for turning out one trick ponies. In software development, for example, computer programs that only do one thing might be given this name. Many kitchen devices, such as a rice cooker or an egg cooker, are also labeled with the term because they are designed for a very specific function and nothing else. If a program or tool performs its one task very well, however, it might be considered valuable despite its apparent limitations.
The phrase is also sometimes used to refer to commentators and academics who use the same material repeatedly without variation; they could also be called "one note." A politician could be accused of being a one trick pony if he or she focused exclusively on one issue while ignoring others. While single-minded pursuit of a goal might seem admirable, it can also suggest that someone does not have a wider grasp of the world, which could ultimately prove to be a problem.
In music, the name "one hit wonder" may be used to mean the same thing as a one trick pony. In this sense, an artist or band releases one very popular song, but cannot repeat the initial success. The term can also be used to describe an artist or band with limited abilities or range. In this case, all of the band's songs might sound the same, and the artist relies on one special feature to attract fans.