um. i would just like to say that i use kali, and that every time i connect the IP address show up, but its always different. why is that, i thought IP addresses were supposed to stay the same?
Aside from the static and dynamic posted about previously byrb300+ (good post too) there are also rollovers. When you connect to busy sites they are often using multiple servers to handle the traffic. DNS's can be set up to use different types of access to these multiple servers so that on DNS entry can be used for many servers. The easiest, and most common, is the roll over. If you have three servers where Server1 has IP1 etc. Then the first time your DNS name (URL) is resolved by your DNS it will return IP1, the second time IP2, third time IP3, fourth time IP1 again, and so on. This spreads out the load without requiring a ton of URL's. There are also load balancing algorithms that work similarly but are more efficient where the servers are actually polled for availability.

One excellent example you can see this with is Yahoo. If you resolve yahoo's DNS name a number of times you will get different servers almost every time. There is just no way one server could handle the sizeable load a site like Google or Yahoo have to deal with. BTW for this type of setup the servers used to be required to have static IP's. When I set up this type of system I had to fat finger in the IP addresses. Newer DNS's may allow more dynamics but I seriously doubt it for this type of implementation.