4G means “fourth generation.” It is the fourth generation wireless
standard, and comes after 2G and 3G. 4G will be different from its
predesessors in that it will be an all IP-based network with download
speeds up to 128 Megabits/second. For you, this will enable seemless
service and access to to faster and higher quality voice and data, as
well as high definition video.
See also: Is 4G different from 3G+?