"Germs" is a catch-all term that covers bacteria, viruses, and other microscopic particles like fungi and protozoa (like an amoeba), that cause illness in humans. Bacteria are microscopic, single-celled organisms. Many don't cause disease and are even beneficial, although some are disease-causing (pathogenic). Viruses are even smaller than bacteria.
Biolight is able to reduce the germ contamination in drinking and/or swimming pool water below the permitted values - sometimes even to a non-detectable level. The Biolight effect can be measured with the ORP (Redox) meter. The higher the ORP level (>665 mV) the better the water can destroy contaminants.