Permanent Dye: They allow for significant hair color change, cover 70%-100% of gray hair, and last for 4-5 weeks, during which time the natural shade begins to show from the scalp.
Temporary Dye: They don't change the hair color, they simply allow for a subtle change in shade, lasting less than 4 weeks.
Alcohol-free: Does not contain alcohols that may cause dryness or irritation.
Paraben-free : Does not contain preservatives that are used to protect the product from microbes and spoilage. Usually preferred by people who want a "milder" formula or avoid certain preservatives.
Sulfate-free (SLS/SLES-free): Does not contain sulfates (sulfate salts/strong cleansing agents such as SLS or SLES), which create a lot of foam but may dry out or irritate hair and skin. Usually considered a milder formula.