What does bandwidth mean?

The bandwidth counts the total amount of data “interchanged” between the web server and the computers of those who view your website.

The more data is downloaded by the visitors, more will the used bandwith grow. To avoid an excess of bandwith use it's recommended to optimize the files that the visitors will see, for example reducing the size or quality of the images of the website, avoid the excess of images shown at the home page, avoid the use of background music or avoiding to host the videos in the same hosting server, using external services like YouTube or Vimeo.