Minecraft worlds are made of blocks and they are the unit of every part of the enviroment.
Bloco terra

Blocks are the basic units in Minecraft, and are essential to the gameplay. Together, they build up the in-game environment, and can be mined and utilized in various fashions.

This mod adds several new blocks to the vanilla Minecraft block-list to make new biomes, new worlds, new traps and the Tubes System.

For more information about Minecraft's blocks: