I'm referring to what people have called "everflux". To me this is really all about "fresh" tags. If you update your content very frequently Google tends to spider your site every day. One day you'll see your site high in the serps and you'll have a date ("fresh tag") next to your URL at the bottom of your listing. Then you'll look again a day or so later and your listing is gone. A search will find it deep in the serps and without the "fresh" tag.