Fluctuation (noun). a wavering; unsteadiness; as, fluctuations of opinion; fluctuations of prices. Fluctuation (noun). the motion or undulation of a fluid collected in a natural or artifical cavity, which is felt when it is subjected to pressure or percussion.iktionary (0.00 / 0 votes) Rate this definition: fluctuation (Noun). A motion like that of waves; a moving in this and that direction. the fluctuations of the sea. fluctuation (Noun). A wavering; unsteadiness.