Ankit, you have very nicely explained the difference between SEO and SEM. I understood them to be part of it each other, but never gave it a proper thought. Search Engine Optimization (SEO) is a technique that helps raise up our (search) rank bring more traffic to our website. While Search Engine Marketing (SEM) is a larger concept that includes SEO as well. Internet Ads are an important component of SEM.
The other star feature of the Domain Vs. Domain tool is it provides you with a detailed report on the competitors’ domains. You can see all the common keywords their domains are associated with and compare their website’s position for each keyword to your own. This allows you to get some insight into what is working for the competition and mimic their success by optimizing your ad strategy and content marketing.