This concept allows for the fact that our economy relies upon natural capital (air, plants, biosphere) and social (human) capital to function. The problem is that much of what our economy needs does not appear on the cost sheet so isn’t valued as it should be.
The following video explains this idea in simple terms
You can also look up associated accounting methods that allow the full costs of production to be accounted for – see https://en.wikipedia.org/wiki/Environmental_full-cost_accounting
This next video is a fantastic fast-based gallop covering the related idea of green design