Accelerando (Italian for “accelerating,” marked accel.) is an instruction for a gradual speeding up of the tempo. It is the mirror opposite of ritardando and a powerful means of building energy, motion, excitement, and dramatic tension.
Accelerando is skilfully used to “drive” the music toward a turbulent climax, to convey a rising of feeling, the whirl of a dance, or unstoppable motion. Many folk dances (notably the Ukrainian kozachok and the Hungarian csárdás) are built on precisely this — from a slow, stately beginning to a frenzied, whirling finale. Combined with a crescendo (a growth of loudness), accelerando creates a sense of an inevitable, captivating surge. Together with ritardando it makes tempo a living, flexible, “human” means of musical expression.
