The term “Markup” describes the code used to construct a website. In fact, there are several languages used to bring a website to life.
Markup is a deceptively difficult process for a myriad of reasons, not the least of which is the mountain of compatibility issues between web browsers. Internet Explorer, FireFox, Chrome, Safari, Opera, and all of their mobile variants will interpret markup differently!
The good news is that if you purchase a site built into a content management system then it rests on our shoulders to get the markup right–letting you concentrate on leveraging your website to achieve its purpose.