banner impressions? how so many?

Ok, so I have 2 banners on my site The site isnt completely launched yet, so basically its just me clicking on them to make sure every thing is working.

Each have 18 clicks, ok, thats fine but can someone explain the impressions to me? I have 17, 420 impressions for one, and 18,000 on the other, what does this mean?

Thanks Derrick

I noticed the same issue with my site. But it's not a big deal for me cuzz I prefer to use a third party option anyway.