An inorganic compound with the formula NaOCl, that is sold as a 5.25% aqueous solution known as bleach ("ultra" bleach is a 7.25% solution.) It is a useful and inexpensive oxidizing, bleaching, and disinfecting agent. It is made very cheaply by running electricity through a saturated solution of table salt (sodium chloride). Sodium hypochlorite, when exposed to excessive light or heat above 40 deg C, will decompose into sodium chlorate and sodium chloride, or sodium chloride and oxygen gas, depending on the pH.
When mixed with hydrochloric acid, it will evolve deadly chlorine gas. Ammonia mixed with sodium hypochlorite evolves nitrogen trichloride instead. Nitrogen trichloride smells like chlorine (and is nearly as deadly!), leaving some people to believe that ammonia and sodium hypochlorite equals chlorine.