A Dictionary of Music and Musicians/Movement
MOVEMENT. A definite and complete item in a musical composition, sometimes forming part of a large work, and sometimes single and independent. So called because each portion as a rule maintains the same rate of 'movement.' On the other hand, a 'number' in an opera or oratorio will often contain several movements. This latter expression is sometimes used instead of it, as in Schumann's 'Faschingsschwank,' which is to all intents and purposes a sonata in five movements, though numbered as if it were a series of separate pieces.
[ J. A. F. M. ]