Yeah I have found a few sites online that give out valuations on your sites and estimate your traffic value ect. In my experience these numbers can be way off. Is this where you got this info from?
I imagine that these sites try to predict the maximum amount of money that is possible for your site to generate according to the amount of visitors you get. For example, say the maximum amount a visitor could spend would be $100, and you get 5 visitors, it will assume your site is worth $500 Like i said i'm only guessing with this but it sounds right lol
I think its related to PPC ie if you'r getting 100 organic clicks and the cpc is $5 the SEO traffic value is $500