The Overworld is the main gameplay area which consists of six islands, spread across an ocean.
This is the island all new players start on. Nothing special. It has trees worth 40 resources, rocks worth 250, and no animals unless they wander over from other islands. There are also several Explorer Book finds. The very basic tools and all but one backpack is sold here. Slug Island is also the exclusive home of the Pebbles resource, which holds 200 resources.
The main island. It will have the most tomb and meteorite spawns because of how large it is. Also contains many Explorer Book finds. Has multiple wild animals, but the only one that can harm you is the Badger which spawns at the top of the Sacred Grove (the large mountain). There are multiple bases and checkpoints, and almost every Machete, Pickaxe, all Fishing Rods, and all but one backpack is sold here.
A small island to the west of Hardwood Island. It has a few gold rocks and multiple 500 HP skeletons. Contains multiple Black Trees and Volcanic Rocks worth 500 resources each.
A swampy island to the east of Hardwood Island, and south of Minnow Island. Has rocks worth 150 resources and trees worth 400. All machetes, backpacks, and pets are sold here - this is the only island that sells pets. It is the home to many frogs, and venomous snakes - they can kill you.
This island is the gateway to the Land Before Explorers, which becomes accessible after two rebirths. Also contains a few dinosaurs which can kill you.