CertNexus Exam CFR-310 Topic 6 Question 38 Discussion

The host that owns the IP address sends an ARP reply message with its physical address. Each host machine maintains a table, called ARP cache, used to convert MAC addresses to IP addresses. Since ARP is a stateless protocol, every time a host gets an ARP reply from another host, even though it has not sent an ARP request for that reply, it accepts that ARP entry and updates its ARP cache. The process of updating a target host's ARP cache with a forged entry is referred to as poisoning.

https://www.researchgate.net/publication/221056734_Securing_Layer_2_in_Local_Area_Networks