An amplifier is a circuit which amplifies the weak signal and raises the amplitude of the signal. An oscillator is a circuit which generates the AC waveforms of particular frequency for providing source to an electronic circuit. Op amps are very common in electronic applications, but you are also face many problems when use them. For example, why do op-amps oscillate? Here is the case analysis and its solutions.
Source: https://www.kynix.com/Blog/Operational-Amplifier-Oscillation-Analysis-with-Circuits.html