Dropbox is software that syncs your files online and across your computers
Put your files into your Dropbox folder on one computer, and they'll automatically appear on any of your other computers that also have Dropbox installed (Windows, Mac, and Linux too!). You can even download Dropbox apps for your smartphone or mobile device (iPhone, iPad, Android, and BlackBerry). Everything in your Dropbox is available from the Dropbox website, too.