What is the meaning of the word "accelerando"?

Definitions:

  1. a gradually increasing tempo of music copy to clipboard noun
    • Across the threshold and down the length of a long hall, the pianist moved with accelerando toward the stage, slipping into the wings before the applause reached full crescendo. copy to clipboard
  2. gradually increasing in tempo copy to clipboard adjective
    • Across the threshold and down the length of a long hall, the pianist moved with accelerando toward the stage, slipping into the wings before the applause reached full crescendo. copy to clipboard
  3. with increasing speed copy to clipboard adverb
    • Across the threshold and down the length of a long hall, the pianist moved with accelerando toward the stage, slipping into the wings before the applause reached full crescendo. copy to clipboard