So, the best way – is to start from IPTV definition:
IPTV (Internet Protocol Television) is a system where a television is transmitted using Internet Protocol all over network infrastructure. A general definition of IPTV is television content that, instead of being delivered through traditional radio and cable formats, is received by the viewer through the technologies used for computer networks.

So in few words – IPTV is a new generation of Television.

The main merit of IPTV – is interaction of video services and availability of wide range of additional services, such as Video on Demand (VoD), TVoIP, Time Shifted TV, Network Personal Video Recorder, Electronic Program Guide (EPG), Near Video on Demand. Besides, IPTV include a package of additional services. They are: Video Telephony, Voting, Information Portals, Web, Games, MOD KOD.

A little from History of IPTV:

In 1994, ABC’s World News Now was the first television show to be broadcast over the Internet, using the CU-SeeMe videoconferencing software.

The term IPTV first appeared in 1995 with the founding of Precept Software by Judith Estrin and Bill Carrico. Precept designed and built an internet video product named “IP/TV”. IP/TV was an MBONE compatible Windows and Unix based application that moved single and multi-source audio/video traffic, ranging from low to DVD quality, using both unicast and IP multicast RTP/RTCP.

In 2006, AT&T launched its U-Verse IPTV service, comprising a national head end and regional video-serving offices. AT&T offered over 300 channels in 11 cities with more to be added in 2007 and beyond. While using IP protocols, AT&T has built a private IP network exclusively for video transport.
Today almost all plots of land penetrate IPTV. Streaming video software today more and more become part of everyday’s life.