The document discusses renewable and non-renewable resources. It defines renewable resources as those that can replenish through natural cycles, such as oxygen, fresh water, and solar energy. Non-renewable resources are divided into those that can be recycled, like metals, and those that cannot due to fixed quantities and our inability currently to recycle them, like coal and natural gas. Sustainable yield is defined as the highest rate at which a renewable resource can be used without reducing its available supply or causing environmental degradation.