Providing a precise definition of Biostimulants is the task of Ebic (European biostimulants industry council):
"Biostimulants contain substances or microorganisms whose function, when applied to the plant or rhizosphere, is to stimulate natural processes to increase or improve nutrient absorption, tolerance to abiotic stress, and crop quality."
Biostimulants are substances typically extracted from plants or microorganisms used in agriculture that act on natural physiological processes, helping the plant to "do better." Biostimulants do not actively counteract attacks from pathogens or phytophagous insects. They make the plant stronger against abiotic stresses such as heat, cold, or water deficiency, increase nutrient absorption efficiency, and improve crop quality.