I’ve always thought it’s the total number or whatever instances the engine creates to function. I mean EVERYTHING; just slate alone running the UE interface consists of thousands of objects alone…
The editor is made out of smaller editors, not all of them are running simultaneously. Thanks to that modularity you will be seeing the number of objects go up and down as objects take up memory and release it, too. When you finally detach your project from the editor by packaging it, you’re not taking those spare object with you. One of the reasons the editor can run quite a bit slower than the final product.
The outliner shows what you yourself have instantiated. There’s more to it, ofc. If you ever feel like diving deeper:
Anyway, 100k are rookie numbers. 