The Global Sand Observatory Initiative (GSOI) is UNEP/GRID-Geneva’s response to requests to identify knowledge gaps under the UNEA-4 Mineral Resource Governance resolution (UNEP/EA.4/Res.19). The discussion on the impacts of sand and gravel extraction, recycling, use, and re-use is a new issue for the international community. This technical report draws on the rich and diverse body of terms from different stakeholders. Within the framework of the GSOI, UNEP/GRID-Geneva reviewed and assessed this terminology. An expert group was convened in December 2020 to begin a series of technical discussions on “what is sand”? This document reports on the first discussion structured around four key terms: 1) sand; 2) gravel; 3) rock; 4) aggregate and a set of associated terms. This discussion was moderated under the Chatham House Rule. As such, no particular view or comment is attributed to any one participant. Following the UNEA-5 Minerals and Metals Management resolution (UNEP/EA.5/Res.12), this living document will be updated as required, and in consultation with UNEP/GRID-Geneva’s experts network.