Cork is a lightweight, spongy material that comes from the bark of cork oak trees, which grow mainly in Portugal and Spain. When you pull the cork out of a bottle, you're holding a piece of tree bark that's been dried and shaped. Cork is waterproof, floats beautifully, and springs back when you squeeze it, which makes it perfect for sealing bottles and keeping liquids fresh.

Cork oak trees have thick, rubbery bark that can be carefully stripped off without harming the tree. The same tree can provide new cork bark every nine years or so, making it a remarkably sustainable material. For centuries, winemakers have used cork stoppers because they seal bottles tightly while still letting tiny amounts of air through, which helps wine age properly.

Beyond bottle stoppers, cork appears in bulletin boards, floor tiles, shoe insoles, and even spacecraft heat shields. Its natural cushioning and insulating properties make it incredibly useful. When you pin a drawing to a corkboard, those thousands of tiny air pockets in the cork grip the pin while protecting the wall behind it.

The word can also mean the act of sealing something with a cork: a chef might cork a bottle after pouring from it.