Simply, a site which is built using Adobe Flash programme, instead of being hand created. This kind of site is bad for search engines on any major term and you will not normally find it gaining ground.
Until late 2008 Google did not index Flash at all. Therefore if you have a site which is built entirely in Flash you were precluded from the search engine index. This now is not the case if you simply have a site which has elements of Flash built in. The indexes will be able to see this and rank your site accordingly.
As with everything related to SERP’s (Search Engine Ranking Positions), the engine really wants to see text. However, in the real world, the viewer would like to see more imagery, and so a combination of the two elements is normally acceptable. The mix of text to graphic (as a ratio) is paramount to your rank.
How do you know if you have one?
Simply right click on your mouse and you will see a box with “settings” and “about Adobe Flash” on it. If this is the case then your site will not rank on major terms. If you have been sold a web site on the basis of it ranking on the engines and it is entirely Flash based, then you should talk to your web designer!
How Can I Combat This?
You will have to look at “artificial” methods to get your site on to page 1, such as Pay Per Click (PPC) or AdWords. This, combined with link building to your site, may help, but is not guaranteed. The alternative is to have your site re-built in HTML/PHP/ASP/Java/Jquery or any other known language and simply add Flash to it as appropriate to get the balance right.
As with all things in “seoland” the engines algorithm (or mathematics) it uses to rank your site may change, and Google, particularly, may change their stance on this. But as this article is written this is their stance.