See resource here.

The GBS is a corporate biodiversity footprint assessment tool: it can be used to evaluate the impact or footprint of companies and investments on biodiversity. The results of assessments conducted with the GBS are expressed in the MSA.km2 unit where MSA is the Mean Species Abundance, a metric expressed in % characterising the intactness of ecosystems.
To link activity, pressures and impacts, the GBS uses peer-reviewed tools such as EXIOBASE, an environmentally extended multi-regional input-output model, or GLOBIO, a model assessing the impact of various pressures on biodiversity intactness.