This indicates whether the client's IP-to-MAC binding in the DHCP security table was learned statically(1) or dynamically(2) via DHCP snooping. Admins use it to distinguish manually configured bindings from ones the switch learned automatically by snooping DHCP exchanges, which affects how the binding should be maintained. For example, a binding manually entered for a server with a fixed IP would show static(1), while one learned from a client's DHCP lease would show dynamic(2).