Robert is correct that you need to install the terminal plugin. I would recommend using the most recent version which is available from the Eclipse release update site associated with the version of Eclipse you have installed.
If you are using Oxygen, then go to http://download.eclipse.org/releases/oxygen.
You can find product documentation on the topic from Atelier as well. Go to Help > Help Contents > InterSystems Atelier User Guide > Tasks > Installing the Eclipse Terminal Plug-in.