Opacity

The terminal window can be made transparent through the Opacity-setting. Note that this controls the transparency of the entire window, including the title bar.

From 0 (invisible) to 100 (opaque).

Global

{
    "Opacity": 80
}

Per App

{
    "Apps": [
        {
            "Name": "Terminal",
            "Opacity": 80,
            ...
        }
    ]
}

Suggested by ukWaqas