This podcast explains what it is and how to use it. Like Starsan, it was originally developed for the dairy industry, but has found favour in the homebrew fraternity. I prefer starsan, although it goes cloudy quickly in our water. Basic Brewing [the podcast] has an episode on startsan too where the creator of starsan spends most of the interview saying that acidified bleach is the best cleaner/sanitiser...some people think is because he is basically saying use it not starsan or iodophor!