It must be HTML text. Some search engines will catalog ALT text and text in comment and meta tags. To be safe, a straight HTML description is recommended. Generally, most people will already have those words present on their pages, but may not also have them in page titles. The lack of success with some search engines does not mean that the site isn't being found.
Many people find the site by entering more words.
The addition of just one extra word can suddenly make a site appear more relevant, and it can be impossible to anticipate what that word will be. The best bet is to focus on your chosen keywords but to also have a complete description. These keywords should be in the text of your site and in the Meta tags. You can also use these same keywords when you submit your own site to search engines. If there are no links to inside pages from the home page, it seems that some search engines will not fully catalog a site.