What is a .com or .net?

A "top-level" (or TLD) domain is what comes after the last dot in a webname. The most commonly known top-level domains are .com, .net, .org and .au. The top level domain types .com, .net and .org have been around for several years (since the Internet took its current form). Most of the possible (and comprehensible) domains have been allocated from those domain types. There are also country-specific top-level domains, such as .uk for the United Kingdom and .au for Australia. The .au country-specific TLD is one of the best regulated (see AUDA) TLDs and all domains within it are precisely and comprehensively allocated (thats our job!).