I was always baffled by it myself, but I was never curious enough to google it. As far as I can tell, it’s not much in use any more. I remember it was fairly common in the 80s, though.
Wikipedia says: In 1970, graphic designer Tom Doerr selected the lower-case Greek letter lambda to be the symbol of the New York chapter of the Gay Activists Alliance. The alliance’s literature states that Doerr chose the symbol specifically for its denotative meaning in the context of chemistry and physics: “a complete exchange of energy–that moment or span of time witness to absolute activity” The lambda became associated with Gay Liberation, and in December 1974, it was officially declared the international symbol for gay and lesbian rights by the International Gay Rights Congress in Edinburgh, Scotland. The gay rights organization Lambda Legal and the American Lambda Literary Foundation derive their names from this symbol.
When I lived in Washington DC in the late 80s the Lambda Rising Bookstore was in Dupont Circle. They closed in 2010 because LGBT books were now carried in regular bookstores.
A funny story about the letter μ. It is also used in the abbreviation for microgram (μg). One time we had to explain to a young lady from the marketing department upstairs that it was the greek letter mu and not the latin letter u. From then on, she referred to micrograms as muligrams.
Was coming in to say that – it may have derived from a statistical notation but it reached common usage at least in the business community as the name of a process-improvement toolset.
Statistical process control is a valid and useful technique and everyone in manufacturing should at least know about it, It works very well. But I cannot look at the words “Six Sigma” without being outraged by the ridiculous marketing bu*****t it has been turned into.
