The word scherzo means a joke or a jest. It often refers to a movement which replaces the minuet as the third movement in a four-movement work, such as a symphony, sonata, or string quartet, though it may also refer to a fast-moving humorous composition which is not part of a larger work.

The scherzo itself is a rounded binary form, but, like the minuet, is usually played with the accompanying Trio followed by a repeat of the Scherzo, creating the ABA or ternary form.

Video examples:
William Porter – Improvisation: Four Modal Variations on Salve Regina: II (Scherzo)