What is meant by the term saponification as related to carpet cleaning?

DEFINITION: Saponification, in carpet cleaning, is a chemical reaction between the detergent and certain oily soils in the carpet.

These oils are vegetable/animal fat and oil from cooking, body oils, etc. Oils like these will react with alkali to form soap. An example of this is how soap was made in the frontier days. The mother would heat up a kettle of bear grease in a big kettle with water. The grease would just melt and float on the water because it hates water. She then added lye or wood ash alkali, and the fat was turned into soap, which not only dissolves in water but also is a detergent! This is another reason that higher pH usually results in better cleaning.