What does "crescendo" mean?

Crescendo: With a constantly increasing volume of voice; with gradually increasing strength and fullness of tone; -- a direction for the performance of music, indicated by the mark, or by writing the word on the score.

Additional senses

  1. 2.(a) A gradual increase in the strength and fullness of tone with which a passage is performed. (b) A pssage to be performed with constantly increasing volume of tone.

Sources