When you think about "theme" several notions should come to mind that distinguish a theme from a mere "keyword".
A "Theme" is a word or phrase that is meant to be given "top-level" importance throughout the overall content of your website.
It is usually the "headword" of a great many long tail keywords that will be dispersed throughout the content and articles of your site.
For example, if "bicycle" is the theme of your website (www.bicycle.com), it would be the headword.
Subthemes and subtopics might be be long tails such as "bicycle tires", "bicycle accidents" and "bicycle helmets".
However, if the overall theme of your website is "bicycle helmets" (www.bicyclehelmets.com), then "bicycle accidents" may be a subtheme of your website.
Theme Zoom helps you design a website blue print that is based on vertical market research.
In general (but not always) your website architecture will reflect your broadest themes at the top levels of the hierarchy.
It is for this reason that we teach "silo structure" and "silo website architecture".
By broadest theme we mean the keyword phrases that have the highest traffic and/or the highest number of competing websites.
Although a keyword phrase of theme may be highly competitive, there is a strong possibility that you have very low "silo competition".
Silo competition is where other websites also utilize your specific topic or theme within the directory structure of their website.
While most top ranking websites for a broad topic or theme contain many pages with this theme, much fewer website contain the theme within a silo directory within the website.
It is very easy to check your "silo competition" for a given keyword or theme.
Simply go to www.google.com and type in:
Google will return the number of websites that contain this keyword, theme or phrase within the URL.
To learn more about this, please study Silo Competition.