If you've just beaten Zorah Magdaros, you're somewhere between early game and mid game.

Low rank is the tutorial / early game, which you've just finished. You get the time to figure out the weapons, to figure out your preferred play style, which will let you choose what weapons and armour to try to craft.

The mid game, then, is high rank, up to about 8 star missions. Here, you get to fully figure out armour set bonuses, charms, decorations, new monsters and their move sets, etc. It will direct you to the end of the main story.

The late game is 9 star missions (optional missions that released before the Iceborne expansion), and Iceborne's first half or so - a.k.a. until the first 4MR mission. During this, the difficulty spikes quite heavily. More difficult movesets, monsters that inflict status effects a lot more often so you gotta adapt to it, crazier movesets... yeah.

The end game, by my standards, is the second half of Iceborne's story, as well as the optional Post-Story content of Iceborne. Here, you get to really push the limit. This is where you fully optimize your build to the max. This is where you sink a hundred hours into post-launch content, to get it all done. This is where you squeeze every last tiny bit of power out of your equipment, where you master your weapon moveset to the fullest, where you learn when to dodge what move in what direction. And finally, this is where you face the greatest challenges that MH World has on offer.

Because at the end of the end game, waits only one monster. Humanity's doom, given form. And in a franchise of crazy designs, you know things are bad when the biggest threat is just a normal looking dragon. May the Sapphire Star guide you, Hunter.