A passacaglia is a musical form characterized by a repeated bass line or harmonic progression, over which variations are developed. Originating in the late Renaissance and flourishing in the Baroque period, it often features a slow, stately tempo. The structure allows composers to explore creativity while maintaining a sense of unity. Typically, a passacaglia is written for instruments such as the violin, cello, or organ, and it can also be found in orchestral works. Notable composers like Johann Sebastian Bach and Henry Purcell have utilized this form, showcasing its emotional depth and intricate variations.