The term "phantom" has several meanings, depending on its context.
In general usage, a phantom refers to something that is imaginary or illusory - it appears real but is not actually present or tangible. For example, one might say they saw a ghostly apparition or an optical illusion and describe it as a "phantom".
In medicine, the term can refer to a sensation or pain caused by damage to a nerve or tissue, which may persist after the original cause has healed. This is known as phantom limb syndrome when experienced by amputees who still feel their missing limb.
The word "phantom" can also be used in a more specific sense to refer to a particular type of musical instrument - specifically, one that produces sound through the use of vibrating air rather than strings or percussion. This is known as an aerophone and includes instruments such as the flute, oboe, clarinet, and saxophone.