Information about FIR Filters

Hello. i am a stundent from an university in Greece and i am working on my graduation. i need some help because i have to answer some question about Filters in my graduation. I can't find information about one of them and this is the cause i am writing here.

the question is: The FIR filter oscillations are observed on both the passband and the stopband frequencies. What is the effect on the output signal and how is it treated? Please justify your answers by giving possible examples.

Can anybody helps me please?

Thank you very much for your time.