A top-level domain (TLD) is the suffix at the end of a domain name — .com , .net , .org , .io , and hundreds of others. Every TLD is operated by a registry, a separate organization responsible for maintaining that TLD's official record of who owns what.

TLDs matter for two practical reasons. First, availability: the same second-level domain can be registered separately under different TLDs by different people ( example.com and example.net aren't the same registration). Second, price: each registry sets its own wholesale cost, which is why .com and a newer or more specialized TLD can differ substantially in price. See At-Cost Pricing, Explained for how that wholesale cost flows through to what you pay.