What is organic fertilizer?

Organic fertilizer, simply put, refers to carbon-rich materials primarily derived from plants or animals, which have undergone harmless treatments such as fermentation and composting, and are applied to soil to provide plant nutrients and improve the physical and chemical properties of the soil. 
It differs from the chemical fertilizers we commonly refer to. Chemical fertilizers are inorganic salts synthesized chemically, offering single nutrients but with rapid effects; whereas organic fertilizers include the following major categories: 
Traditional farmyard manure: such as human and animal excreta, straw compost, wood ash, and oilcake fertilizer (soybean cake, rapeseed cake).  
Commercial organic fertilizers: factory-produced refined organic fertilizers, bio-organic fertilizers (with beneficial microorganisms), and organic-inorganic compound fertilizers.  
Green manure: green plants directly incorporated into the soil, such as purple clover and sesbania.  
Its core function is not only to supply nitrogen, phosphorus, and potassium, but also to replenish soil organic matter and nourish soil microorganisms.