It is actually fairly simple. A Musician is a person who does something related to music for a living. Whether it is vocal or intrumental performances, the person is still considered to be a musician as long as they are doing it as a profession. Musicians can travel around the world and tour, playing with groups or as a soloist, and earn money by doing so. This lifestyle is more of the famous musician lifestyle. However there are other types of musicians that are part of musical groups who do not tour yet still play for people depending on what they specialize on.
The life of a musican can be both very time consuming and very layback. If the musician is constantly touring and making new music to perform, then they are going to have a busy life style do to how much time that process takes. However if the musician is just part of an ensomble then there is not as much time spent besides the amount of time of practice needed and the amount of time spent performing. This is not as long term as touring though.