Split-horizon
Split horizon is a concept that is used by distance vector dynamic routing protocols as a routing loop prevention mechanism. It simply states:
"Never send routing information back in the direction from which it was received."
So any routing information that was received via a particular interface will never be sent out that same interface.
EIGRP and RIP are among the routing protocols that use this mechanism.
Links
https://networklessons.com/eigrp/troubleshooting-eigrp-route-advertisement