Well the only reason I asked is because I am unsure how Google Adsense works. My website mentions the word "gallery" very often, especially in the new section... yet it still prefers to pick up on "joomla" and "content management systems" etc.
Yes, that is correct.
One the home page there are some that are remotely linked to photography, the rest of the pages (such as my build your own gallery page) are only related to CMS.
What ads show up on your page largely depend on your content and what ads are in Google's database. They try to do the best they can with matching but if there are no ads directly related to your content then they try to get as close as they can.
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Don't put the cart before the horse. Plan your website, thencreate it.
As lisa said, Adsense directly feeds ads related to your on page topics and phrases you obviously have the word CMS or Joomla listed somewhere on one of your pages.