Ok basically what he is saying is your website might be generating clicks from a keyword which has more potential if it moved up the rankings a little.
So he is saying take all the keywords from Google analytics which generated a click from organic (say over a 3 month period) and paste them into Adwords keyword tool as exact match.
You might find a keyword which generated 20 clicks actually has a monthly search volume of 5,000.
Because this keyword has 5, 10, 20 clicks it must not be that far away from page 1 as users don't really dive deeper then page 2 of Google (in general) and your getting clicks for it.
So that would be a good keyword to aim for in your SEO efforts (as long as its relevant to your industry).
If you find a keyword like this, you could most likely search for it in Google and find your result within the first couple of pages.
Hope this makes sense.