What is the meaning of sustainability when it is applied to the use of natural resources and economic activity?

When applied to natural resources and human activity,
sustainability refers to practices that will achieve a given economic or social goal
without excessively depleting the natural resources available in an
area.

For example, sustainable agriculture is agriculture
that does not deplete the soil or otherwise cause a given area to become unsuitable for
agriculture in the long run.  For example, agricultural practices that try to reduce
erosion are sustainable.  By contrast, a type of agricultural practice that allows
topsoil to be carried away by wind and/or water is not sustainable because this practice
will deplete the soil, causing the land to no longer be
fertile.

Sustainability also refers to other economic
activity.  The main idea simply is that sustainable economic activity is activity that
does not destroy the natural resources needed to carry out that
activity.