Oscillator

What Does Oscillator Mean?
A technical analysis tool that is banded between two extreme values and built with the results from a trend indicator for discovering short-term overbought or oversold conditions. As the value of the oscillator approaches the upper extreme value the asset is deemed to be overbought, and as it approaches the lower extreme it is deemed to be oversold.

Investopedia explains Oscillator
Oscillators are most advantageous when a clear trend cannot be easily seen in a company's stock such as when it trades horizontally or sideways. The most common oscillators are: the Stochastic oscillator, RSI,  ROC and MFI.