Technically, biofilms are a conglomeration of bacteria, fungi, algae, protozoa, debris, or corrosion products embedded in a self-produced and secreted matrix of extracellular polymeric substances (EPS). The EPS can be composed of polysaccharides, proteins, nucleic acids, and lipids. Essentially, biofilm may form when bacteria adhere to surfaces in aqueous environments and begin to excrete EPS, a slimy, glue-like substance that can anchor them to all kinds of material - such as metals, plastics, soil particles, medical implant materials, and tissue. Once anchored to a surface, biofilm microorganisms carry out a variety of detrimental or beneficial reactions (by human standards), depending on the surrounding environmental conditions.  One example of beneficial reaction is the application of biofilm to degrade vinyl chloride, a toxic solvent that have contaminated groundwater and endangered a drinking water resource.

The biofilm functions as a protective hydrated barrier between the bacterial cells and their environment. It facilitates survival under harsh conditions and environmental insults such as ultraviolet radiation, physicochemical stresses, desiccation, and insufficient supply of nutritive resources. For these reasons, in nature most microbes live as communities in biofilms.

On the other hand, since bacteria in biofilms are more resistant to antibiotics, biofilm formation on in-dwelling medical devices and damaged tissue, such as catheters and prosthetic joints and heart valves, is an ongoing medical concern. For the industry, biofilms cost the billions of dollars yearly in equipment damage, product contamination and energy losses. The biofilm phenomenon impacts a wide range of industries, including petroleum, specialty chemicals, health, household products, drinking water, mining, and utilities.