Web hosting bandwidth is the measurement of data being transmitted through your web server at a given period of time.
Having adequate bandwidth is very crucial to the success of your site because it will affect your site visitor's experience, especially when there are high traffic levels. Every visitor that views a page on your site is consuming bandwidth because they are downloading and uploading information to the web server. Thus, in order to accommodate high daily traffic levels you will need ample bandwidth. This is the primary reason why bandwidth is one of the two most important web hosting features to consider when shopping for a new plan.
Bandwidth is perhaps the most important because it dictates how many visitors your website can handle during a single time period.