An unpleasant, sticky brown substance used to glue leaves, grit and grass clippings to the underside of someone's shoe. Like its blue-coloured namesake, it is most easily picked up, (sadly only by conscientious dog owners), by rolling another piece of brown-tack from the same pile over it. Dog dirt.
Hey, buddy, what's that smell? Dang, someone must have stood in some brown-tack!