From a technical perspective, most sources define an organic fertilizer as a substance that is derived from animal or vegetable matter.  From a functional perspective, many sources consider an organic fertilizer as a substance whose primarily function is to feed microbes in the soil, versus feeding the plant.  The microbes in turn break down minerals and nutrients to feed the plant.  The term 'living soil' is often used to describe a soil-based ecosystem that is capable of producing a large part of a lawn's nutrient needs, especially if grass clippings are recycled.

In contrast, chemical fertilizers are synthesized nutrients that are added to the soil to feed the plant directly.  The nutrients in chemical fertilizers act quickly with moisture and can make a bad lawn look better, faster than most natural fertilizers, a desirable trait in today's world of instant results.  However, a common consequence of over-applying chemical fertilizers is to kill off the microbes present in the soil, thereby destroying the soil structure and its capability to naturally produce nutrients for the plant life.  Turf growing in these conditions essentially become chemically dependent  on the constant addition of synthetic nutrients to sustain their health.