Feather

Alright, you may call me a dummy, but in the three years (or so) I have been using Photoshop, I've never used the "feather" tool.

Now, I've read a couple of tutorials here and they talk about the feather tool a lot and I was just wondering... what does feather do exactly or if it has many uses? What would be the main use then? Just a little confusion I would like to straighten out.

Thanks!
Oh yeah, I use Photoshop 7.0