PVPP (Food Grade Polyvinylpolypyrrolidone) fining agent. Basically it's an electrostatically charged plastic polymer that adheres itself to chill-haze forming tannins and oxidized compounds. Also removes polyphenolic compounds and oxidized melanoidins. It works and works well, in fact if you go over the recommended dosage, you will start to strip color and good melanoidins (flavor) from your beer so watch out. I would start with 1/4 oz. per 5 gallons and see how that works (for beer....use half that amount for wine). Oh, it will also drop most or all of your yeast out, so I would say only use this if you are force carbonating.
Usage: Mix recommended amount in 2 cups of preboiled water (that is still hot enough to sterilize the Polyclar) or a pint of beer. Pour into your secondary, and stir the whole batch well with a sanitized dip tube, racking cane. Give it a few days to settle (you should be able to see it work) and rack off of the sediment.