It's like a screen that goes in front of the mic that helps filter out plosives. Here's what one looks like: http://www.sweetwater.com/store/detail/MASSB/Kirk, I am pretty clueless wrt recording, what is a pop filter?
You can do a home-made one with at hanger and nylon stocking too, or whatever you can think of...it just slows down the air and pop filter isn't a cure-all either. Becoming conscience of which constants cause plosives can help you control them too.