Tar is a thick, black, sticky substance that comes from heating wood, coal, or petroleum. It's so sticky that if you step in fresh tar, it clings to your shoe like super-strong glue.

For thousands of years, people have used tar to waterproof things. Sailors once coated their wooden ships with tar to seal the gaps between planks and keep water from leaking in. They also tarred their ropes to protect them from rotting in the salty ocean air. (In fact, British sailors were sometimes called “tars” because they worked with tar so often.) Today, tar mixed with gravel becomes asphalt, the black material used to pave roads and driveways.

You might hear someone say they'll tar and feather a person who did something wrong. This refers to a cruel punishment from history in which people were covered in hot tar and feathers. Today it just means punishing or criticizing someone harshly.