Used as a verb it means to bleach the hair and remove current color.
When used as a noun it refers to the chemical composition designed to remove color from the hair. Bleach is sometimes referred to as a pre-lightening or decolorizing treatment.
Daily Hair Tip
Embeth Davidtz was discovered by Steven Spielberg while decked out in a huge bouffant hairdo for a TV film. Davidtz comments "I'm grateful he got past that hair"