What does rumination mean?

I ruminated too much this morning and got distressing mental images (and confirmation) which sent me spiraling again. How do I stop thinking about this and how do I get back to myself? I feel destroyed.

I've been doing well the past month in cutting down on compulsions and have been feeling better however, last night I had a set back that carried on into today. I had gotten very poor sleep (4ish hours) and then something triggered my memory. I think with the sudden anxiety spike and lack of sleep I didn't have the strength to ignore my compulsions. Last night and today I've realised I've gone back into rumination and mentally reviewing the event excessively again and comparing my situation to other people's, but most of the times that I start going down these rabbit holes I don't even realise I'm doing it? Also been fixating a bit on the fear that I've ruined my progress and that I will fall back into the deep end of it all again, that I have done so much work getting myself out of, although trying my best to not be too discouraged. Does anyone have any advice on how to deal with rumination more specifically?

I've been told it's impossible to "push intrusive thoughts away", but also that rumination is a compulsion. What is rumination vs. overthinking? And how do I stop ruminating properly and healthfully?