Terraformers are Machines with the ability to change the terrain around them. The affected area is a little larger than 8 chunks by 8 chunks. The reasons for terraforming are usually to add a desired visual effect that is naturally not possible (Chilling - snow in the nether). Or to change a large area without having to manually do the alterations (Cultivation - turn a desert into a vast cropland).
Note that the Terraformer is an IC2 Block/Item, so it requires EU instead of BC power. The Terraformer must be removed with a wrench to be removed properly. Using a wrench on the Terraformer gives back the current TFBP in the Terraformer, so the second usage of wrench removes the Terraformer.