"Uninstalled processes" in the "App history" tab of Task Manager

If you go to the App history tab of Task Manager on Windows 8 or newer and then enable Options | Show history for all processes, you'll probably get an extra entry called "Uninstalled processes" that took a few resources.

The name might be a little confusing, but from what I can tell, that entry displays the sums of all the resources used by processes launched from executables that can no longer be found. You can test this theory by making a copy of a standalone program, running it for a while, then deleting it. The things it used will be added to the "Uninstalled processes" row.

Based on my Super User answer.