TLD is an abbreviation for top level domain. It is the extension or portion of a domain name that follows the dot.
You are likely most familiar with TLDs like .com, .net, and .org. These TLDs are designed to signify something relevant to the domain. For example, .com stands for commercial
and .net stands for NETwork.
There is also what is called a ccTLD, or country code top-level domain. These are designed to signify sites located in or associated with certain countries or territories. Most of the ccTLDs actually don't have restrictions regarding who can register domain names. In fact, many ccTLDs are commonly misinterpreted as TLDs. For example, while .tv is commonly registered by television and media related websites, .tv is actually the ccTLD designated for the country Tuvalu. Domain hacks are also a popular use of both TLDs and ccTLDs. This involves creating a full word or phrase when combining the domain name with the
TLD to create something your audience will easily remember. A popular example is using the .me ccTLD for Montenegro and combining it with "aweso" to create the domain aweso.me.
There are also second level domain options, particularly popular with
ccTLDs. For example, the United Kingdom has a number of second level domains ranging from '.co.uk' (designed for United Kingdom based businesses) to '.net.uk' (designed for UK-based internet providers).