what is the meanig some time ago?

hello, what dose the feeling of some time ago giving to you? is it same with long long ago or once upon a time?
thank you for your explanaition.

‘Some time ago’ = a considerable amount of time before now. It is not as long ago as ‘long ago’ or ‘once upon a time’, but it is all relative:

Of meals: ‘I’m quite hungry-- I had breakfast some time ago’. (= 4 hours)
Of evolution: ‘All of the dinosaurs died out some time ago’. (= 65 million years)