ARP resolves IPv4 addresses to MAC addresses within a local subnet. ARP request (broadcast): "Who has 192.168.1.1?" ARP reply (unicast): "I do — here's my MAC."
ARP operates at Layer 2. ARP table caches IP-MAC mappings. ARP poisoning inserts false mappings to redirect traffic (MITM). Dynamic ARP Inspection (DAI) validates ARP packets against the DHCP snooping binding table. 'arp -a' displays the local ARP table.