https://viroliegy.com/2022/06/16/purification-virologys-black-sheep/

PURITY: Relative freedom from extraneous matter in the finished product, whether or not harmful to the recipient or deleterious to the product. (21 CFR 600.3(r)) FDA Guidance Definition for vaccine purity
The above definition for purity is taken from the FDA’s Guidance for Industry. According to the FDA, purity is considered relative freedom from extraneous matter. What is “relative freedom?” Relative implies that something is true to a certain degree. In other words, there is freedom from extraneous matter to a certain degree. However, in relation to purity, there can be no degrees of freedom from extraneous matter. A substance is either pure, meaning that it is free of all contaminants and foreign matter, or it is impure, meaning it is mixed with contamination and foreign matter. There is no such thing as purity to a certain extent yet you will commonly find discussions of purity within the “scientific” papers as if this can be the case. Terminology such as low purity, partially purified, somewhat purified, relatively purified, highly purified, etc. are thrown about as vague descriptors used to wiggle around a concept that is so simple and straight forward that most children can understand it. Something is either pure or impure. There is no in-between.
