DropBox is online file synchronization
Dropbox is a piece of software that you install on your computer (or on your Mac, your smartphone, etc.). You specify which directory is synchronized, and everything that is in it is automatically synchronized. This is very useful if you have multiple computers, or if you are in school one time, and the other time back home. With DropBox you have those files available everywhere, and by default you have 2GB available for free (more space to buy). There are similar services, but DropBox is user friendly and just works. Also create an account with DropBox
DropBox explained [YouTube] W4eTR7tci6A [/youtube]