Fluctuation (noun)

1. The act or an instance of fluctuating; a change or variation.
2. The extent of change or variation.
3. An irregular or unpredictable movement or change.

Origin:

Mid 17th century: from latin fluctuat- "beat, tossed about", from the verb fluctuare, from fluctus "a wave".

Examples:

1. The stock market had a large fluctuation today.
2. Her moods had frequent fluctuations.
3. The temperature had a fluctuation throughout the day.
4. The price of gas had a fluctuation throughout the week.
5. The level of the lake had a fluctuation with the amount of rain.