A biocide is a chemical substance capable of killing different forms of living organisms used in fields such as medicine, agriculture, forestry, and mosquito control.A biocide can be:
A pesticide, which includes fungicides, herbicides, insecticides, algicides, molluscicides, miticides and rodenticides.
An antimicrobial, which includes germicides, antibiotics, antibacterials, antivirals, antifungals, antiprotozoal and antiparasites. See also spermicide.
Uses
Biocides can also be added to other materials (typically liquids) to protect the material from biological infestation and growth. For example, certain types of quaternary ammonium compounds (quats) can be added to pool water or industrial water systems to act as an algicide, protecting the water from infestation and growth of algae. Chlorine can be added in low concentrations to water as one of the final steps in wastewater treatment as a general biocide to kill micro-organisms, algae, etc. It is often impractical to store
Source:
http://en.wikipedia.org/wiki/Biocide