The top-level domain, TLD for short, is the last part of the internet domain name; is in other words the alphanumeric code that follows the 'point' to the right of the URL; for example, the internet address of the Italian wikipedia is it.wikipedia.org and therefore falls within the top level domain org.

The Internet Numbers Authority (IANA) currently ranks the top-level domains in three different types:

• Country code top level domains (or ccTLD): Used by a state or territorial dependence. It consists of two letters, for example JP for Japan and IT for italy, or EU for the European Union;
• Generic top-level domains (or gTLD): used (at least in theory) by a particular class of organizations (for example, com for commercial organizations). This suffix is three or more letters. Most gTLDs are available all over the world, but for historical reasons, GOV, MIL and EDU are reserved, respectively, to the government, the army and educational institutions;
• Top Level Domains infrastructure: The top-level domain harp is the only existing one.