from the French “Groupe de Rapporteurs”; signifies any of the permanent working parties subsidiary to WP.29 (e.g. on noise, lighting, pollution and energy, passive safety, etc.)
GRSP
Working Party on Passive Safety (cf French: Groupe de Rapporteurs sur la Sécurité Passive)
GTR
Global Technical Regulation
IWG
Informal Working Group: A group of experts authorized to develop proposals for consideration by WP.29 without being bound by formal UN rules of procedure.