Bridge

A bridge is a protocol for moving assets between blockchains. Chains are isolated. Bitcoin cannot send value to Ethereum natively. A bridge creates a path. The usual method is lock and mint. You lock assets on Chain A. The bridge mints matching assets on Chain B. Later you burn the Chain B tokens and release the originals on Chain A.

Example: move bitcoin to Ethereum as WBTC. You lock BTC with a custodian. They mint WBTC on Ethereum. You can trade WBTC and use it in DeFi. When you want BTC back, you burn WBTC and the custodian releases BTC. Bridges are how capital reaches Ethereum lending, trading, and yield from other chains. The weak point is custody. If the custodian is hacked or malicious, the bridge loses funds.

Most large bridge hacks have been custody failures. Bitcoin can't directly transfer to Ethereum. The mechanism is locking and minting. Bridges are required for cross-chain DeFi. You can access Ethereum's biggest lending protocols, trading protocols, and yield opportunities from any blockchain.

org warns that bridges are a common hack target because they lock large pots of tokens while minting wrapped copies on another chain.