Glossary
Composability
The property that lets smart contracts freely call and build on one another, so protocols combine like money legos into new applications without permission.
Composability is the ability of on-chain programs to plug into each other: any contract can call any other contract's public functions in the same transaction, and anyone can deploy new logic on top of what already exists. Because protocols share the same state and settlement layer, a deposit in one app can be used as collateral in a second and swapped through a third, all atomically.
This is why DeFi protocols are often called "money legos" — a new app can treat Uniswap, Aave, or an ERC-20 token as a public building block rather than reimplementing them. The trade-off is shared risk: a bug or price manipulation in one widely-used component can cascade through every protocol that composes with it.