There are two variants of the 4G technology: WiMAX and LTE.
WiMAX is in operation since 2006 in some parts of the world, LTE is a rather nascent technology that conventionally offers very high spectrum efficiency and data speeds (100 Mbps in download and 50 Mbps in uploads).
LTE is based on 3GPP standards, which is an advancement or extension of 2G and 3G standards, making it backward compatible to existing 2G and 3G networks.
[Mbps is Mega bits per second. Thus 100 Mbps download speed means 12.2 Mega Bytes of data per second; Similarly 50 Mbps upload speed means 6 Mega Bytes Per Second. Thus on 4G, a 720 MB movie will take just under a minute to download]
Compared to 3G, 4G offers a more efficient way of transferring data and the price of transferring data is much lower.