The Italian word Allegro means fast, joyful, lively. In music this is one of the most common rate corresponding to a very short step. Often in tempo Allegro composers of the XVIII - XIX centuries wrote the first movements of sonatas and symphonies. Therefore, the form in which they are written. sometimes called a Sonata Allegro. Such, for example, the first part of the symphonies of Haydn, Mozart and Beethoven.
C. A. Mozart. Sonata 15 in C major (K.545).
Part 1 Allegro