The coal/charcoal iron is an ancestor to the modern electric iron. While today's irons use electricity to heat their metal bases and to generate steam, coal/charcoal irons were heated by smoldering coals which were taken from a fire and placed inside a box on the top of the iron. The lid of the box had a handle which allowed people to hold the hot iron as they ran it over clothing, smoothing out wrinkles. There are paintings dating back to over a thousand years ago depicting women using an early coal/charcoal ironing process.
People would place coal/charcoal in a metal pan and run it over silk and other wrinkled fabrics. In the western world, people ironed their clothing with "sad irons, " which were extremely heavy iron bars with handles that were heated in a fire. People would take the iron out of the fire, holding it with a cloth. However, these sad irons were poor performers because they cooled quickly and required constant reheating.
These coal/charcoal irons stayed hot longer than sad irons and were easier to use. The coal/charcoal iron had to have holes or vents along the sides to allow the coals to get enough air to continue burning. The irons are also still in use in some developing nations where electricity isn't is cheap and accessible.