http://www.3gpp.org/about-3gpp/about-3gpp has information about the generations of mobile systems. 5G will be the latest generation and isn't 100% formalized.
> The introduction of 5G will be the result of improvements in LTE, LTE-Advanced and LTE Pro, but this will soon be followed by a major technology step, with the prospect of an entirely new air interface. The first drop of 'New Radio' features, in Release 15, will form the first Phase of 5G deployments.
> Full compliance with the ITU’s IMT-2020 requirements is anticipated with the completion of 3GPP Release 16 at the end of 2019 - In Phase 2 of the 3GPP 5G effort.