Some uses for lye include making soap and detergent, relaxing hair, and processing natural gas and gasoline. Lye is also used in papermaking and for neutralizing acids. It is also used to process soft drinks and to peel fruits and vegetables chemically.
Lye is used in the processing of aluminum. Aluminum is found in bauxite ores, and lye is used to dissolve the bauxite and reveal the aluminum. Lye is famous for its ability to clear clogs out of drains, though this needs to be done with care, since lye can corrode pipes. It is also useful as an oven cleaner.
Lye is also used to make grits, bagels and a Scandinavian delicacy called lutefisk. It's also used in the preparation of pretzels, green olives, Chinese noodles and century eggs.
Lye soap can be made at home; the soap no longer has to be an unattractive and utilitarian block. Lye soaps can now be made with essential oils, as of 2015, and can be formed into attractive shapes.
One interesting use of lye is as an ingredient in a "green" funeral. Instead of burial or cremation, the corpse is dissolved in lye and the resultant slurry is simply discarded.
Lye is formally sodium hydroxide, or NaOH, or potassium hydroxide, KOH.