Definition of "fluctuation"

fluctuation

/flʌkt͡ʃuːˈeɪʃən/

noun
countable and uncountable, plural fluctuations
1. A motion like that of waves; a moving in this and that direction; an irregular rising and falling.
  Quotations
  The scientific instruments of the day recorded rapid fluctuations in the Earth's magnetic field, as powerful electrical currents flowed through the upper atmosphere.
  2023 November 15, Prof. Jim Wild, “This train was delayed because of bad weather in space”, in RAIL, number 996, page 30
2. A wavering; unsteadiness.
3. In medicine, a wave-like motion or undulation of a fluid in a natural or abnormal cavity (e.g. pus in an abscess), which is felt during palpation or percussion.