What is that big white flash used for dark environments?

I went to a nightclub recently and there was a professional photographer taking AMAZING pictures with his dSLR. I noticed he had a big white square flash mounted on it. (It wasn't the conventional flash with the clear glass, it was like a non-transparent white plastic cover.)

What is that flash? Any more info on this would be appreciated.

It was probably a soft box. Take a look below, Jeff

http://www.lumiquest.com/lq925.htm

Yes yes yes yes!

Thank you!

What do you think about it? Is this something pros use? Is it worth the investment?

ALSO, which one should I get for shooting people indoors, either in office or at parties, etc.?

Whoa whoa tiger :D hold your horses ! First we have identified what it is; now you need to identify if it's something you would like to use once reading up on it.

It can be used by anyone, and is definately worth the investment especially for making the on-board flash useful in a variety of situations.

What it does is diffuse the light (make it softer) coming from the flash to make the shadows less hard in the photo the softbox was used.

http://en.wikipedia.org/wiki/Soft_box

There's many varieties of uses of them, hell you can even make your own.

http://www.diyphotography.net/homest...ounted-softbox
there's a DIY site on how to make your own, cheap flash mounted softbox. Hell anything can be used to make a softbox, there are pro kits you can buy that range between 500+ $ and infinity.

http://www.instructables.com/id/DIY-...m-an-umbrella/
another DIY someone made a softbox out of an umbrella. It actually can be very fun to make your own to see what you can accomplish with it and experiment with how light bounces around and how to use that in making your photos.