Soap terminology decoded, including the phrase that does not mean anything

The vocabulary trips up almost everyone at the start, partly because one common phrase is genuinely meaningless.

• "Lye soap". All soap is lye soap. Soap is what you get when a fat reacts with a strong alkali, and there is no soap without it. When somebody asks for lye soap they usually mean handmade rather than commercial, or they are thinking of a harsh old-fashioned bar. Worth answering the intent rather than the words.
• Saponification. The reaction itself. Once it is complete there is no lye left in the bar, which is the point people are usually asking about.
• Superfat, or lye discount. Deliberately using slightly less alkali than the fats need, so a small amount of oil remains unreacted. This is what makes a bar feel mild rather than stripping.
• Trace. The point where the mixture thickens enough that a drizzle leaves a mark on the surface. Light trace pours; thick trace does not.
• Cure. Weeks of drying after the reaction finishes. Not about safety, which is settled in a day or two, but about hardness and how long the bar lasts in use. Rushing it gives you a soft bar that melts away.
• Gel phase. The batch heating itself through as it reacts, which changes appearance rather than quality.
• Ricing, seizing and soda ash. Fragrance reacting badly, the batch setting far too fast, and a harmless white powder on the surface respectively.

The label point: what you may legally call a product varies by country, and words like moisturising or antibacterial are often regulated claims rather than descriptions. Check locally before selling anything.