A chain is a series of connected metal rings or links that form a flexible but strong line. Each ring loops through the next one, creating something that can bend around corners but is difficult to break. You might see chains holding swings at a playground, securing a bicycle to a rack, or pulling heavy loads.

Chains work because of how the links connect: each one relies on the others, and the whole chain is only as strong as its weakest link. That's why people say “a chain is only as strong as its weakest link” when they mean that one weak part can cause the whole thing to fail, whether they're talking about an actual chain or a team working together.

The word also describes connected series of other things. A chain of stores means multiple locations owned by the same company, like a pizza chain with restaurants in different cities. A food chain shows how animals depend on each other for food: grass feeds rabbits, rabbits feed foxes. A chain of events means one thing leads to another in sequence, like dominoes falling.

As a verb, chain means to fasten or restrict with a chain. You might chain your bike to prevent theft, or feel chained to your desk when you have too much homework.