Allegro is:

• a direction in musical notation indicating that the music is to be played fast and lively. See tempo.
• the Allegro Low Level Game Routines, a cross-platform computer game programming library.
• a charter airline that operates both international and domestic flights from its base in Mexico City.
• a name of a Polish online auction website
• The 1947 musical by Rodgers and Hammerstein
• The Austin Allegro a car once manufactured by British Leyland