HTML is simply tags in a text file that tell the browser how to display a page. So you would think your HTML web page should look the same to everyone, however, browsers can interpret those tags any way they want and in fact they do. That is why poorly design websites may appear nice in one browser but look very poor in another browser. That is because not all browsers follow the HTML standards 100%.

So why is this important to know? Well it should be quite obvious. When developing a web page you will want to check it in several browsers. You may choose to check it in a wide majority of browsers but this can be time consuming. You may check your web page in only 10 of the most popular browsers or use some web stats on you site to check what are the most popular with your visitors.

If you are wondering who sets the standards for HTML it is World Wide Web Consortium (W3C). They are concerned with web standards and guidelines. If you are starting out learning you may find this site hard to learn how to code HTML. This site is designed to explain HTML standards. You may want to search for an HTML tutorial instead.