Biomes

Environments (or Biomes) are different types of landscapes located around a Terraria world. The most common ones are Forests and Deserts, located on the surface. Going farther left or right will eventually lead to the Corruption. Underground environments are also present and even the occasional sky environments.

Corruption
Each and every world has a corruption. Most worlds generated have around 2-3. Most small worlds which are generated have two corruptions, usually with one in either direction from the spawn point. It is best to avoid the corruption during the earlier stages of the game, as the monsters which spawn in the corruption are both powerful and can also spawn regardless of the time, during night or day. The purple grass of the corruption can be removed with Purification Powder, and the spreading of the corruption can be prevented by either placing any block other than dirt at its edge, or by planting a Sunflower, which can be found randomly in the world, or they can also be bought from a Dryad. The purple stone found in the corruption is called Ebonstone, and can only be mined by a Nightmare Pickaxe or higher.