What does Bleach mean?
A chemical used to make denim fade.
Heddels explains Bleach
The term bleach refers to a chemical used to lighten or remove color, usually through the process of oxidation. A versatile substance, bleach is most often used as a disinfectant, sterilizer, or whitener. While there are many types of bleach, the most common are sodium hypochlorite, hydrogen peroxide, and calcium hypochlorite.
Here is a container of bleach: