Definition - What does Split Horizon mean?
The split Horizon technique transmits the data packets in forward direction and propagates to all the attached nodes, except that router which sent the new update. This technique prevents routing loops and also sublimates those areas, where Route Poisoning cannot avoid routing loops to occur. This technique is integrated in most of the distance vector routing protocols including RIP, IGRP, EIGRP and VPLS.
Techopedia explains Split Horizon
Split Horizon is a technique integrated within majority distance vector routing protocols that prevents these routing loops to occur within a network by discarding the address of the source update router, from the list of all routers which it will propagate an update, received from the source router. This technique is similar to route poisoning, which prevents network traffic to flow from a faulty/invalid path.