STP Loop Guard
STP Loop Guard can provide additional protection against layer 2 loops. An STP loop can happen when a port that is in the STP blocking state changes into a forwarding state.
Loop Guard Can Add Additional Checks
In the case that the designated port stops receiving BPDU’s then that port is moved into a STP Loop-Inconsistent state rather than in the Listening > Learning > Forwarding state. Without STP loop guard the port would assume the designated port role.