SEARCH VOLUMES AND COST PER CLICK
This is an average of the total searches that people have performed for a given keyword per month, over a given period, normally 12 months.
In terms of domain names, it is the average number of searches people have done of your domain name per month over a given period of time.
You can determine the estimated search volume (actual number of visitors to your site) by taking the search volume shown on the Google Adwords Keyword Tool and then multiplying it by how many searchers in Google will actually click on your website. The higher you rank, the more searchers will click on your website.
So basically, If your website keyword gets more searches, the more you earn from your website.
Cost Per Click
The cost per click (CPC) is the amount that advertisers are paying for a single click for this keyword in Google AdWords, in this case, your domain names.
If you plan on monetising your site with Google Adsense, then you must give this a proper consideration. As a result, Finding a keyword that has an average of $1 CPC or more is always beneficial.