What exactly does 'endgame' mean in Stellaris, the matches don't actually have time limits, right, eh?...

Cause that'd be kinda, i don't know, stupid, eh?

Or is the word I'm looking for pointless, eh.

Another thing, I keep hearing about fleet stacks getting up to 157k strength, but I have yet to see one over 17k, and the 17k one was an unbidden fleet, that was smashing my 10k Imperial Navy into the dust, eh... R.I.P. Eh-questrian Star Empire Mk1, eh.

5256501
I think the end game is when you kill/ally all other factions, if not then I think there is no end.

5256501 Kill/Ally with all other factions or control 80% of the habitable planets on the map. Those are the 'win' conditions.

You can see your progress on the situation window. At the bottom there is a tab which I believe is labeled victory conditions and it will show you how many opponents and planets are left until victory.

5256501 Rival or declare war on a Fallen Empire if you want see fleets upward to 100k.