undulation

/ˌʌndʒəˈleɪʃən/
noun
  1. A smooth, wavy motion or movement like that of waves.
    • The snake's undulation was so smooth it seemed to float.
    • We watched the undulation of the tall grass in the wind.
    • The undulation of the sea made the boat rock gently.
  2. A wavy shape, form, or surface; a series of rises and falls.
    • There were gentle undulations in the carpet where it had been folded.
    • The artist captured the undulations of the desert sand dunes.
    • The road followed the undulations of the hills.
  3. A fluctuation or variation in level, intensity, or amount.
    • The undulation of the stock market worried investors.
    • The undulation of her voice added drama to the story.
    • There was a noticeable undulation in the temperature throughout the day.