I've recently purchased a book on Quantum Physics, and I'm trying to get the basics down. At this point in time, I'm reading up on how Planck proposed that oscillators can only oscillate at discrete energies as opposed to on any amount of energy (on a theoretical continuous spectrum). This came up in his attempt (and success) to solve the black body radiation "problem." However, I don't exactly understand what "oscillator" means in this context. I understand that to oscillate is to move uniformly back and forth (so to speak) over a center point. But I'm confused as to why the word oscillator is used here. Any help is appreciated. Thanks!