You are looking into a broadcast storm and want to get to the root cause of the incident. Doing this investigation, you realize that the cause was more than one layer 2 path between two endpoints. This is an example of what?
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Answer Description
A switching loop occurs in computer networks when there is more than one layer 2 path between two endpoints. This situation can result in broadcast storms when broadcast packets are sent over the loop due to the packets being sent out of every port on the switch then being repeatedly rebroadcast.
Wikipedia
A switching loop or bridge loop occurs in computer networks when there is more than one layer 2 path between two endpoints (e.g. multiple connections between two network switches or two ports on the same switch connected to each other). The loop creates broadcast storms as broadcasts and multicasts are forwarded by switches out every port, the switch or switches will repeatedly rebroadcast the broadcast messages flooding the network. Since the layer-2 header does not include a time to live (TTL) field, if a frame is sent into a looped topology, it can loop forever.
A physical topology that contains switching or bridge loops is attractive for redundancy reasons, yet a switched network must not have loops. The solution is to allow physical loops, but create a loop-free logical topology using link aggregation, shortest path bridging, spanning tree protocol or TRILL on the network switches.
Switching_loop - Wikipedia, the free encyclopedia 