For .COM, .NET, and .ORG names. The organization responsible for the actual administration and maintenance to a top-level domain is known as the registry. The registry is where registrants or registrars go for new or modify domain name requests. This is a US government contracted database. Most TLD registries require initial registration fees as well as annual or bi-annual renewal fees.
Prices vary from cost-free to thousands of dollars per domain depending on the TLD chosen.
This pricing structure is likely to change in the year 2000. One through ten year registrations will become available with different pricing tiers. Renewal Registration for most domain names needs to be renewed based on some scheduled yearly interval. Second level domain names are what you register in a Top Level Domain registry. In the example YourCompany.net - the YourCompany part is the second level domain while the .net is the Top Level Domain.