The Corruption

The Corruption is an ominous environment. Purple corruption spreads over nearby dirt blocks, Grass blocks and trees, and Thorny Bushes sprout, making it a difficult land to traverse. Deathweeds can be found here. Purification Powder can be used on corrupted dirt to turn it into grass, and Sunflowers can be placed to stop the corruption from spreading further.

Many chasms dot the landscape in the Corruption. It is recommended that you don't explore these until you have a Grappling Hook or some other form of vertical transportation, as chasms can be hundreds of feet deep. Chasms are covered in Ebonstone Blocks which can only be mined using a Nightmare Pickaxe or better, or by using Dynamite, which also destroys Shadow Orbs. Alternatively, Purification Powder can be used to turn the Ebonstone into normal Stone Blocks which can be mined with any pickaxe.

Caves can often be found surrounding the chasms. In these caves, Pots, Chests, Life Crystals and Demon Altars are common.

Corruption vs. "The Corruption"

 * Corruption is a purple grass-like substance that infects grass blocks and spreads quickly to any connected Grass blocks, similar to ordinary grass.
 * "The Corruption" is a term used to describe the biome that takes effect when a significant amount of Corruption exists in an area of the World; theme music is changed in such areas (to The Corruption's theme), Trees turn purple, the sky darkens, and corrupted enemies like the Eater of Souls spawn.

A small amount of Corruption can exist in other biomes, the same way Jungle Grass can exist in biomes that are not yet actual Jungle biomes, and Meteorite blocks can exist in biomes that are not Meteorite biomes. A multitude of any of these in an area will cause the respective biome to exist though, with altered theme music and spawned enemies appropriate to those environments.

Getting through
The Corruption is infamous for being hard to get through. Here are a few pointers on making it through:
 * Defend yourself. Make sure you have at least Copper Armor, or better yet, Iron Armor.
 * Have good weapons. Ranged weapons are useful in taking out the Eaters of Souls and his closely related friends, especially if you use piercing ammo.
 * Don't fall down chasms. The deep Corruption chasms are a surprisingly large danger, so either get something to help you jump over, such as a Cloud in a Bottle, or get some blocks to make a bridge.