Google NEXTGEN or search on FAA.GOV web site. It is a set of technologies, infrastructure, procedures, etc designed to modernize aviation. We are moving away from ground based radar surveillance and separation of air traffic. As many have already commented, several technologies comprise NEXTGEN:

C-Communications
N- Navigation
S- Surveillance

GPS/WAAS/GBAS/GLS
RNAV RNP AR with RF legs
ADS-B Out (mandatory for most aircraft by 2020)
ADS-B In (optional) but will facilitate receipt of pretty close to "real time" traffic, weather reports and wx radar info
CPDLC- Text Messaging of ATC instructions/clearances

Boeing calls the NEXTGEN package "FANS" = Future Air Navigation System.