cinnamon mouse to left corner gives grey screen with plus sign on left

[sdowney717]

it is supposed to show the open window.

So what to do

the plus sign has a white border and is centered looks like a tab

[entropy1]

You moved your mouse to the "Hot corner". If you click on the + you get another workspace. If you open Cinnamon Settings you can turn the hot corner off or move it to another corner.

[sdowney717]

Yes, I found out what it does. My dad in law who is 79 clicked the plus sign hundreds of times, so the ever shrinking workspaces have dissolved into a grey goo of invisibility.
How can you delete all those extra workspaces?

[sdowney717]

He kept saying his screen dissappeared.
So he must have frustratingly clicked the plus sign over and over.

Since I did not know exactly what he did or what it was in Cinammon, I just told him it was if people want to instantly hide the screen.