First, let’s explain what an IP address is. An Internet Protocal
Address or IP address for short, is like your computer’s phone number.
Without it, your computer wouldn’t be able to connect to the Internet.
Every computer, tablet, smart phone, and Internet enabled device has
it’s own IP address (even some light bulbs have an IP address these
days). An IP address consists of numbers and periods (192.168.1.1).
So, what is a dynamic IP address? Well, a dynamic IP address is one
that changes from time to time and isn’t always the same. If you have a
residential cable or DSL service, you most likely have a dynamic IP
address. Internet Service Providers (ISPs) provide customers with a
dynamic IP addresses because they are more cost effective. Instead of
one IP address always being yours (a static IP address), your IP address
is pulled from a pool of addresses and then assigned to you. After a
few days, weeks or sometimes even months, that number gets put back into
the pool and you are assigned a new number.
This is why a dynamic IP address can make it tricky to remotely
access your PC, DVR or webcam, because even if you know your IP address
at this moment, 5 minutes from now it could be different. So if you are
away and want to access your computer remotely, but you have the wrong
IP address, you will not be able to connect to your computer.
Dynamic DNS makes a dynamic IP address act as though it’s static
(does not change) even though it is not. With No-IP you create an easy
to remember hostname. This hostname is the URL that you type into your
browser to connect to your remote device. Our Dynamic Update Client
takes your hostname that you created (yourname.no-ip.org) and points it
to your IP address. When your IP address changes, our Dynamic Update
Client updates your IP address on our servers, therefore your hostname
stays active with your active IP address and your connection stays
available all the time
Refered From
http://setuprouter.com/networking/what-is-an-ipaddress/