The Hallow

The Hallow is a new "anti-corruption" biome which may be introduced in 1.1. It can be created with Hallowed Seeds and will stop the Corruption from spreading. Biome name was taken from bandcamp page.

Unicorns will spawn here.

It is still unclear whether this biome will actually be included, as it hasn't been explicitly confirmed and named, but only shown on screenshots in dev blog.