Internet Protocol (IP) address is simply a number allocated to every device (whether it’s a home PC or a web server hosting hundreds of websites) which uses the Internet to communicate. The term address is appropriate as it tells other devices where to find the specified device in order to communicate it (which may or may not be possible of course depending on such things as whether it is switched on/accepts communication etc).
As demand for connections to the Internet has increased the development of a new system called IPv6 which is simply a 128 bit system (instead of the current 32 bit system). This allows for a huge number of extra IP addresses to be allocated and the growth of the Internet can then continue unbounded.