Firstborn/Library/PackageCache/com.unity.terrain-tools@4.0.3/Documentation~/toolbox-gizmo.md

Gizmo

The Gizmo is a transparent cube that appears in Scene view to help identify the location and scale of the Terrain. Enable the checkbox to display the Gizmo, and disable the checkbox to remove it. Click the arrow beside the checkbox to display the Gizmo's Edit Bounds button.

You can use the Move, Scale, and Transform tools on the Gizmo in Scene view.