A theme can be defined as many things, like a subject matter or a color theme, but as far as Google is concerned, a theme is defined as the subject matter. The theme is what the web pages are about e.g.a grocery website's pages are about grocery; therefore the site's theme is grocery. Each page might be about some grocery material. The theme of a single page about cabbages is cabbages whereas the theme of a page about potatoes is potatoes, but the site’s overall theme is grocery.

Most of the top search engines including Google like themes to the degree that they affect a page's rankings. Situations always come when a PR6 page can't beat a PR4 or PR5 page in its rankings for a certain search term. Of course there are several reasons for this but the most important one is the theme of the page.

If you were to include a few pages about something completely different then grocery, like toys, then the total 'Page Rank' theme of the site would be weak. You might be offering this to facilitate the people visiting the page but it would still lower the rank of the site. Nevertheless, some of its Page Rank pages would still be greatly themed but the total site theme would become low. Like in the grocery site example, every page is about a different item of grocery and consequently the overall site theme is grocery. But it isn't cabbages! If some other site comes along which covers only cabbages, its theme would be cabbages and for "cabbage" type of search terms this site has a better chance of beating the ranking of the total grocery site. It might depend on some other factors as well but the primary factor is the theme of the site.

Sites often don’t really cover just a single topic of cabbages or peas. They mostly cover the general information instead of something particular just like grocery. But we can take some steps to improve the theming in different websites and create the most of their page’s' themes.

Suppose that the grocery site deals with cabbages, onions and peas, and all of its content pages have information about all these three products. Then what would be the page’s theme? Or what would be the site’s theme? All of the products have been placed through the site and the pages in a kind of generic fashion, so that each page would be weakly themed towards cabbages, onions and peas. None of these three products would be strong enough in any of the pages. However, the site's theme would almost remain the same.

Now let’s suppose that the site has a quantity of pages which only deals with onions, another group which only deals with cabbages, and a last group of pages for peas. Totally each page would be strongly themed towards all the three products. The overall ranking of the site will not be affected too much as whole.