route poisoning and reverse poisoning are routing loop prevention techniques used by distance vector routing protocols.
"Poison reverse allows routers to break the split horizon rule by advertising information learned from an interface out the same interface. However, it can advertise routes learned from an interface out the same interface with a 16 hop count, which indicates a destination unreachable, "poisoning" the route. Routers with a route with a better metric (hop count) to the network ignore the destination unreachable update."
route poisoning is setting a route's metric to infinity (i.e. max hops
poison reverse is the process of breaking the split horizon rule and sending a poisoned route back over the same interface from which it was learned