Great question — answering as the UphillTech team:
I assume you have linked your Google Webmaster Tools and Google Analytics, and those are the impressions you are referring to. Google counts these each time you search. I've noticed this on sites which have unique names and once we begin testing if it's cached and indexed those appear as impressions. I believe GWT is more accurate than their keyword tool. You can test this buy running a very specific search which will make your website appear in the top 100 and then check the impressions in webmaster tools the next day and you should see it. Run the same search and it'll count another impression.
Full answer by Anagio: https://webmasters.stackexchange.com/a/38737 (CC BY-SA 3.0).
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