PH is a gauge of a liquid's acidity, and the range goes from 0 to 14, with seven being considered neutral. If the pH is less than seven, the liquid is acidic, and if it is more significant than seven, it is deemed alkaline.
In most instances, it has to do with water quality, but it can be used to measure the acidity of other things like blood and urine. All kinds of chemical substances can be measured on the pH scale from battery acid, which is alkaline at 0, or the highest at 14, which is liquid drain cleaner.
Liquid drain cleaner is very caustic and requires the use of protective eyewear and gloves when used. It dissolves gunk in the drain like soap, hair, lotions, creams, and pretty much everything.