Offload
Offloading an app packs the app and its data into an archive on your external drive and removes them from your Mac. It can't be opened until you restore it.
Offloading an app packs the app and its data into an archive on your external drive, then removes them from your Mac. It frees as much space as uninstalling, but keeps everything so you can bring the app back exactly as it was.
It's different from moving an app. A moved app still opens through a shortcut; an offloaded app can't be opened at all until you restore it.
In Storage Studio, Offload is in the Apps window. The originals are removed only after the archive copy has been checked. Offloaded apps are listed on the Offloaded tab — even while the drive is unplugged — and Restore copies the app back once the drive is connected. Restore won't overwrite anything: if something is already in the app's place, it stops and tells you.
See also: Offloading and restoring an app · The Apps window · Relocate