Define
The Internet Protocol, or IP address, is a code that uniquely defines a device that is connected to the Internet. The IP address allows every device to find each other as well, much like a mailing address with the postal system. The code consistes of four numbers, ranging from 0 - 255, and separated by periods. IP addresses are also known as IP numbers or simply as the IP.

Details
In reality, these addresses are actually 32-bit binary numbers, however they appear as four octets (octets meaning they each have eight positions when viewed in binary form) of number characters in decimal form. For example, this computer's particular IP address is 69.235.234.68. When a computer views a website, it swaps IP addresses with the host computer, allowing them to connect and transmit data. IP address correspond to the particular number of the node that is connected to the network, which network it is connected to and which system of the network it is connected to. IP addresses can even reveal the geographic location of a computer. See more at the "What is my IP Address" link in the Resources section. There are also several different classes of IP addresses:

• Default Networks- use IP address 0.0.0.0
• Loopback Networks- use IP address 127.0.0.1 and constantly send a message back to itself for the purpose of diagnosing network problems.
• Broadcast- Sends messages to all computers on a network using an IP address of 255.255.255.255
• Class A- Used for large networks, such as international companies, that uses a lot of computers. IP addresses that begin with the numbers 1 -126 are a part of this catagory. The other three octets are used to identify a host (node) on the network, allowing for a total of 2,147,483,648 unique IP addresses.
• Class B- Used for medium sized networks such as colleges and universities. IP addresses that begin with the numbers 128-191 are used for this type of network. The second octet is used to determine the Net Identifier, and the thrid and fourth octets are used for identifying a host which gives a total of 1,073,741,824 possible unique IP addresses.
• Class C- Used for small to med-size businesses. The IP address that begin with the numbers 192 to 223 are part of this class. The second and third octets are used for the net identifier and the last octet is used to determine the host. This size network allows a possible 536,870,912 unique IP addresses.
• Class D- Used mainly for multicasting (sending a packet addressed to a special group address). This class is different from the rest because its first, second and thrid bit are 1, and the fourth is 0.
• Class E- Mainly for experimental purposes. It is similar to class D in every respect, except its fourth value is 1.

Resources
http://whatismyipaddress.com/
http://www.primusvoip.co.uk/jargon_buster.html
http://www.paessler.com/info
http://www.usr.com/support/2410/24xx-ug/images/AP%20IP%20address.jpg
http://www.howstuffworks.com/