Internet Protocol (IP): The Internet Protocol, defined in STD 5, RFC 791, is the network layer for the TCP/IP Protocol Suite. It is a connectionless, best-effort packet switching protocol.
"An identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route messages based on the IP address of the destination. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 1.160.10.240 could be an IP address." - Webopedia.

Each device on the Internet gets assigned a unique IP Address. No two devices can have the same IP Address.

Your IP Address provides detailed information such as your location, city, state, country, ISP (Internet Service Provider), zip code, area code, longitude and latitude, effectively allowing accurate mapping of your whereabouts.

Although some techniques exist, helping you hide this information though use of anonymous proxies, services such as IPmap.com, showmyip.com and GetIP.com will still be able to accurately identify your IP Address.

There are four non-profit agencies that are in charge of assigning IP Addresses:

• American Registry for Internet Numbers (ARIN)
• RIPE Network Coordination Centre (RIPE)
• Latin American and Caribbean Internet Addresses Registry (LACNIC)
• Asia Pacific Network Information Centre (APNIC)

"Private IP address space has been allocated via RFC 1918. This means the addresses are available for any use by anyone and therefore the same private IP addresses can be reused. However they are defined as not routable on the public Internet. They are used extensively in private networks due to the shortage of publicly registerable IP addresses and therefore network address translation is required to connect those networks to the Internet." - Wikipedia

Although private(internal) IP addresses are non-routable, services such as IPmap.com are still able to detect and identify them.