What the Heck is a Hashtag?!

As you can probably tell from the title of this post, I am not a tweeter, or I don't twitter, or however else you want to say it.  But, I keep hearing about these things called "hashtags" and I always think to myself, isn't that the pound symbol?  You know, on your phone you have the pound "#" button or the star "*" button.  Duh, right?  Wrong!  It's so much more complicated than that!