The Terraformer was/is a tool that was/is used to terraform the environment.
The Terraformer could/can deform and form the environment, useful for digging, and forming bridges.
It has no icon, and is only available through console commands.
The Terraformer's previous model was a green variation of the Flashlight's model. This was changed to have a different model in the Seamoth Update.
For your information, it MAY still be obtainable using console commands.