I think of those old fashioned coffee makers that are made of metal with the glass little contraption on the top where you can see the coffee bubble. I looked it up though and to percolate means to filter through something porous..Maybe with those old coffee makers they are referring to the metal filter that fits on the metal stem that fits into the bottom of the pot. It can go on the stove. There are also electric percolators. My mom had one.I have a big one. A large urn that I bring out for special occasions when a lot of people are around. It is in the basement in a box.