What's the proper name for this problem?

I have come across this network problem twice in as many weeks and it has both times brought the entire network to a standstill. Stopping dhcp requests, stopping printing, stopping internet access.

I never expected this to happen nor had I ever tried it to see what would happen, but I can see how in many networking environments how this would happen!

Basically, both times, different sites, children and staff have plugged a lose network cable from a switch, back into the switch. First time a member of staff did this as she didn't like the lose cable that I had left out of site being there. The internet went down so she took matters into her own hand and looked behind her computers to see a lose network cable, that I had left there for a future PC that would be installed. She plugged the lose cable back into the network, causing some sort of a loop in the network and sending all the wifi points and switches crazy! Everything went back to normal when I unplugged. Same happened in a classroom where a switch had been set up on a table with cables out of it for laptops, as access points do not reach there. A kid who was playing with the cables did the same thing with no less than THREE cables. Same problem.

What is the name for this sort of network problem? I guessed "loopback" but a wiki for this says this is not the case. Any ideas?