A target where a building's carbon emissions - from both its operation (energy use) and its construction (embodied carbon) - are reduced as far as practically possible, with any unavoidable remainder balanced out through offsets or carbon removal, so the net contribution to atmospheric carbon is zero. "Net zero operational carbon" and "net zero whole-life carbon" are meaningfully different, narrower and broader claims, and the distinction matters when a client asks for one specifically.

BIM's role is mainly in the "reduce as far as possible" part: 6D energy analysis and embodied-carbon calculation from model quantities are what let a design team actually test how close to net zero a design gets, long before construction starts.