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 popular in the Baroque period, it often features a slow, stately tempo. Composers like Johann Sebastian Bach and Henry Purcell have famously used this structure in their works. Typically, a passacaglia consists of a series of variations that explore different melodies, rhythms, and textures while maintaining the underlying bass pattern. This form is often found in orchestral, chamber, and keyboard music, showcasing the creativity and improvisational skills of the composer.