With the movie "Sex Tape" out now, and the trailer containing the phrase "Nobody understands the Cloud!", perhaps it's time to give ourselves a definition we can use. Ready? Here goes:
The Cloud is the internet, when marketers want it to sound new.
There. Now you understand the Cloud. If you want to go into more detail, the word "Cloud" is most often used to describe services provided over the internet, such as file synchronisation or database storage. This is, again, because of marketing, but there's nothing new or special about these services except the name "Cloud". The internet was perfectly capable of these services before companies built them, and it's still the internet afterwards. "Cloud" is just their word to make you think they've done something brand new and revolutionary when all they've done is put some extra services online that weren't online before.
Mokalus of Borg
PS - It's faster to say, so I guess that's something good.
PPS - I wouldn't call that quite enough, though.