The Spanning Tree Protocol is a network protocol that ensures a loop-free topology for Ethernet networks. It prevents the formation of broadcast storms and loops in a network, which can lead to network degradation or outages. STP works by designating one switch as the root bridge and then determining the most efficient path from the root bridge to each switch in the network. It identifies redundant paths and blocks some of them to prevent loops. In the event of a link failure, STP dynamically recalculates the topology to maintain network connectivity. Variants of STP, such as Rapid Spanning Tree Protocol (RSTP) and Multiple Spanning Tree Protocol (MSTP), offer faster convergence and better support for larger networks. STP is a crucial protocol for ensuring the reliability and stability of Ethernet networks.