Mobile phones have just become the most popular way of accessing the internet, some people would say. It's increasingly important to consider providing a mobile version of your website that is small, fast and designed for the mobile platforms.
Note that for most the mobile website is not a replacement, computers and their browsers have not gone away.
A web browser is a software application (also known as a computer programme) for retrieving, presenting, and traversing information resources on the World Wide Web.
An information resource is identified by a Uniform Resource Identifier (URI) an example of which is a Uniform Resource Locator (URL), and may be a web page, image, video, or other piece of content. Hyperlinks present (embedded) in resources enable users to easily navigate their browsers to and between related resources.
In June 2010 it was esitimated there were 1,966 million internet users, all using a browser of some type.
As a website designer I am keenly aware that as interpreters of HTML, various browsers do not always display or interpret code in the same manner. I currently test my websites in at least 4 browser types that presently make up over 95% of internet users worldwide. Or more if a client has specific needs.
It's also important to note that computer screeen resolutions can also show up weaknesses. Font selection was limited by available fonts on internet users computers, however it's now technically possible to use almost any font using CSS3. Finding free fonts or buying them and the extra time needed to install them and test them in browsers combined with remaining frustrating formatting issues (such as multiple embedded font requirements for simply bolding some text) mean they are not recommended for the faint hearted or cash straped just yet. Thankfully however the web safe palette of colours is no longer the issue it used to be.
The list of available web browsers on the right is not a complete list, you can find that here.