3GPP is an acronym for the "Third Generation Partnership Project". The goal is to make specifications for a 3rd Generation Mobile System based on the GSM core networks and UMTS.
It is teaming up with ETSI, ARIB, Committee T1, CWTS, TTA and TTC, meaning that only North America is left out. Interesting to note is that Japan now using PDC instead of GSM supports this project.
3GPPs webpage is at http://www.3gpp.org