The word "percolator" has come to mean that special coffee pot that used to sit on Grandma's stove and bubble away like mad all morning long. Typically they consist of a heat proof pot that holds the water, a long tube (like a straw) that holds a filter basket at the top. This filter is normally made of metal and holds the coffee grounds apart from the water in the main pot. Usually fairly oarsely ground coffee is used and a perforated lid is placed over the filter in order to distribute the water evenly over the grounds.