Structure and form do not dominate a rhapsody. Freedom and a flowing nature are more important in a rhapsody, which can be highly personal and inspired by many different feelings and emotions. Improvisations are also common, adding to the personal air of a rhapsody.
Rhapsodies, outside of just music, can refer to any emotional artistic work. Ancient Greeks wrote poems to honor heroic deeds. Musically, rhapsodies were more common during the Romantic era, where works tended to reject strict form and were inspired by emotions.
Actual lengths of rhapsodies may vary, but specifically, they usually contain only one movement. Instead of creating another episode when the mood or style changes, rhapsodies mix various changes in the composition inside a single movement.
Famous and well-known examples of rhapsodies include George Gershwin's "Rhapsody in Blue," which mixes classical music and jazz. Sergei Rachmaninoff and Franz Liszt were Romantic-style composers also known for their rhapsodies, such as Listzt's "Hungarian Rhapsodies."
Rhapsody, as defined among different artistic mediums, comes from a Greek word meaning "songs stitched together," and was first used to describe poetry. The emotional aspect of the definition came in 1639, and it was first used to describe music in the mid-19th century.