A briar is a thorny or prickly plant, especially a wild rose or blackberry bush. If you've ever tried to pick berries from a bramble patch and gotten scratched by sharp thorns, you've met a briar up close.

In stories and fairy tales, briars often create natural barriers. In “Sleeping Beauty,” a thick wall of briars grows around the castle, hiding and protecting the sleeping princess for a hundred years. Real briar patches can feel almost as formidable: dense, thorny, and nearly impossible to walk through without getting scratched.

You might also see the word spelled brier, which means exactly the same thing. People sometimes call a difficult, tangled problem a “briar patch” because it's as complicated and painful to work through as pushing through actual thorny plants.