Here is the hypothetical scenario. You have a website that is highly themed to a particular niche. As an example, suppose your site is all about kickboxing. The site itself is in a portal style, where you have lots of news stories about the latest kickboxing events, profiles of the latest kickboxing champions, reviews of the latest kickboxing styles, etc. Now let us also imagine that the favorite acronym amongst kickboxing enthusiasts is KBX (just made that up). So to be hip and cool, the acronym KBX appears numerous times on the page, but the actual word "kickboxing" rarely if ever is shown. Joe Schmo and Kyle Kicky are well-known champions and they are discussed a lot, and of course all of the kickboxing enthusiasts who see the site know what sport they participate in.
So, you sit back and wonder why the search engines do not rank you well for kickboxing. I see this come up time and time again. Although advice is often given to not think about the search engines, this is not always true. You do have to not only think about the search engines at times, but you have to also think LIKE the search engines sometimes. Put yourself in the bots role. Look at the page as a bot would look at the page. If you were just a dumb robot, would you know that your page was about kickboxing?
If the design of your site is one in which it does not naturally lend itself to including your main concepts (such as lots of news stories), then it would be wise to include a short, static, introductory paragraph above the stories that explain the purpose of the page. Do not make the bots work hard, because frankly they will not. Make it easy for the bots to be able to see past the trees so that they know that they are looking at a kickboxing forest.
