A conversion rate is the percentage of unique website visitors who take a desired action upon visiting the website.
The desired action may be submitting a sales lead, making a purchase, viewing a key page of the site, downloading a file, or some other measurable action.
Our article on the outline for a marketing plan can help you plan your advertising and marketing efforts, and check out our article on what metrics to track (and what not to track) on the LivePlan blog (as well as our entry on website metrics).