Progressive enhancement is a strategy for web design that emphasizes accessibility, semantic markup, and external stylesheet and scripting technologies. Progressive enhancement uses web technologies in a layered fashion that allows everyone to access the basic content and functionality of a web page, using any browser or Internet connection, while also providing those with better bandwidth or more advanced browser software an enhanced version of the page.
This strategy is something I've been employing for a while, but without the terminology to succinctly describe it. As Bliss mentioned, with SWFObject, SWFAddress and the Flash Search Player from Google, it's becoming easier and easier to confidently sell SEO and Flash together. Next time you pitch a client, wrap this process up as "progressive enhancement." It would be nice to make the term an industry standard.