A studio musician is a person who comes in, usually as a contract laborer, and records musical parts for another artist. For example, someone who is primarily a singer may have a whole band of studio musicians who create music for him to record over. Studio musicians are typically very talented individuals with a lot of technical skill on their instruments. Some of them work as part of studio-based bands, while others work alone, and it can either be a full-time job or a part-time job. In some cases, studio musicians are also be asked to go on tour with an artist.
Sometimes studio musicians play common popular instruments, like the guitar or drums, while others play less common instruments, like harps. A guitarist or drummer would typically be called in to record backing tracks for pop, rock, country, or other similar music types. Someone who played harp or flute might be called in for orchestral recordings or to add unconventional instruments to recordings of a popular music band. In either case, the economics of supply and demand will affect the availability of work. For example, since there are so many guitarists, it could be hard to find work, even though there might be a lot of work available, simply because of the huge amount of completion.
There are certain skills that can be particularly useful for a studio musician. For example, most of them have a high level of ability on their instruments because they generally have to be among the best available in order to beat out the competition and get work, and if they are more skilled, they can usually complete their jobs rapidly with very little fuss. There is also a need for versatility because if a studio musician is comfortable in many different music settings, he or she can very likely find many more jobs. Many studio musicians are also able to read music, which helps them quickly jump in and start recording unfamiliar material in the least amount of time possible.
Sometimes a studio musician does recording work as a primary job, but not always. Some of them may also have bands of their own, and they occasionally become famous. For example, Jimmy Page was a major studio guitarist in the 1960s with hundreds of recordings to his credit before he eventually ended up as the guitarist of his own famous band, Led Zeppelin. On the other end of the spectrum, some popular musicians from famous bands will also work part-time as studio musicians, or do occasional session work as a side-job.