A cinder is a small piece of partly burned coal, wood, or other material that's still glowing or hot. When a campfire dies down, the gray and black chunks left in the fire pit are cinders. They look lifeless but can stay hot enough to burn you for hours.

Cinders form when something burns but doesn't completely turn to ash. In old-fashioned coal furnaces or steam locomotives, workers had to regularly shovel out the cinders that accumulated. Volcanoes can throw out volcanic cinders, which are small chunks of lava that cool and harden as they fly through the air.

The word appears in the fairy tale Cinderella, whose name comes from sitting among the cinders of the fireplace where she was forced to work. A cinder block is a building block made from concrete and coal cinders, though today they're usually made without actual cinders and are more properly called concrete blocks.

If something is burned to a cinder, it's been burned so thoroughly that it's completely charred and ruined, like toast left in the toaster too long.