The Crimson is a biome in Terraria Otherworld that was first introduced near the end of the Swing Grappling trailer. It seems similar to its Terrarian counterpart. It may be an alternative infestation to The Corruption just like in Terraria.
The Crimson Axe can be seen during the trailer returning from the original game, but with a different name. Also seen are some Crimson enemies that look and act like Blood Crawlers and Crimeras. The Crimother can also be seen at the end of the trailer.
Similar to The Corruption, the crimson seems to also spread through the dirt in the biome. making the entire ground look red.