List of generic Top level domain names with explanations:

These are generic Top Level Domains. Some of them need special credentials to be registered.

• .aero domain is reserved for members of the air-transport industry and cannot be registered by anyone.

• .biz domain is intended for businesses entities and can be registerd by anyone. Save on .BIZ Domains at GoDaddy.com - $7.99

• .cat domain is reserved for the Catalan linguistic and cultural community.

• .com domain is intended for commercial organizations and can be registered by anyone. It is also the most popular topl level domain name in the world. You can register it right now .

• .coop domain is a tld for cooperative associations. Not very common.

• .info domain is open for everyone to register and is meant to be for informational websites.

• .jobs domain is designed jobs companies and for human resource managers.

• .mobi domain is a more recent domain for websites connected with mobile products and services and for mobile-compatible sites. .MOBI Domains from GoDaddy.com
  

• .museum domain is restricted only for museums.

• .name domain is reserved for individuals that want to establish their name as a brand. It can be freely registered here.

• .net domain is also a popular tld and can be registered by anyone. It is inteded for entities connected with networks, networking.

• .org domain is tld of organizations around the world. It is designed for the noncommercial community, but can be registered by anyone.

• .pro domain is restricted to professionals: doctors, attorneys. Applicant has to provide credentials in order to register.

• .travel domain is reserved for travel related entities and cannot be registered by anyone.

4 special Top Level Domain Name extensions

These four are somewhat special since they are reserved for special needs:

• .gov domain cannot be registered by public. It is exclusive for the United States Government.
• .edu domain is reserved for US educational institutions.
• .mil domain cannot be registered by public. It is reserved for the needs of the United States Military.
• .int domain is used strictly by organizations endorsed by international treaties between governments.