Does it mean the number of unique visitors compete.com estimates they got for the whole month (from the US only) for example, if a site has a count of about 30K for each month, does this mean its estimated to have had a total of 30K unique visitors for the whole month- so, if it is a site that people find once and search maybe a couple of pages each and then never return, the site will have about 60K page views a month or 2K a day if he site has a count of about 30K each month but is a kind of site where people might visit daily and look at several pages then it might have hundreds of thousands of page views every month? and if it has two adwords banners on each page that cost an advertiser $5 cpm each ($10cpm total for both) but then google takes about half then they should be making about $5 for every 1000 page views?
Yes, it's unique visitors. An estimate of that, of course. A site with 30k people count could, as you say, have hundreds of thousands of page views. Compete also gives the page views/visitor estimate that you can use. I have no idea if Google's share is 50%, as they do not disclose it, but I'd estimate it's a bit more.