A fugue is a contrapuntal compositional technique in two or more voices, built on a subject (theme) that is introduced at the beginning in imitation (repetition at different pitches) and recurs frequently in the course of the composition.

David Briggs – Fugue at St. Sulpice
Otto Maria Krämer – Suite Francaise – Fugue
William Porter – O dass ich tausend Zunge hätte – Fugue