Violin is the common name for the instrument in most classical and orchestral contexts, while fiddle is more frequently used in traditional folk music or popular music settings. The term "fiddle" is sometimes used to refer to a specific type of violin with a flatter bridge and a brighter tone, which is often used in folk music.
In general, the differences between fiddle and violin lie in their playing styles, rather than their construction. Fiddles tend to be tuned slightly differently from classical violins, and they are often played in a more improvisational manner, with a greater focus on ornamentation and decoration. Fiddlers may use a variety of techniques such as double stops, slides, and harmonics, which are not as commonly used in classical violin playing.
The distinction between fiddle and violin can also be cultural and regional. For example, in certain regions, the term "fiddle" may be preferred for folk music played on violins, while in other regions, "violin" may be the more common term regardless of the genre of music being played.
Ultimately, the terms fiddle and violin are generally used interchangeably to refer to the same instrument, but the specific terminology used may depend on the context and the individual player's preferences.