The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities.

Domain Name System Block List - a list of IP address ranges or other information compiled as a DNS zone. Information in DNS format is easy to query and transport, and its small answers are very "light" on bandwidth overhead (UDP vs. TCP). A DNSBL of domain names is often called a URIBL, Uniform Resource Indicator, although there are numerous such lists written under other names.