Layer 2s and bridges: key words
Read the word, say the meaning out loud, then open the card.
Layer 2
A separate blockchain that extends Ethereum and settles its transactions on Ethereum. Source
Rollup
A layer 2 that runs transactions off Ethereum, then posts their data back to Ethereum in batches. Source
Optimistic rollup
A rollup that assumes batches are valid unless someone proves fraud during a challenge period. Source
Fraud proof
Evidence, checked on Ethereum, that a rollup batch was worked out wrongly. Source
Challenge period
The time, roughly seven days, when anyone can challenge an optimistic rollup batch. Source
ZK rollup
A zero-knowledge rollup: it posts a cryptographic proof that each batch is correct. Source
Validity proof
A cryptographic proof that a batch's changes really come from running its transactions. Source
Sequencer
An operator that orders a rollup's transactions and posts its batches. Some rollups have a single one. Source
Sidechain
A separate blockchain with its own rules and validators, linked to Ethereum by a two-way bridge. Source
Bridge
A link between blockchains that lets tokens and messages pass from one to another. Source
Wrapped token
A token on one chain that stands for an asset held on another, such as WBTC for bitcoin. Source
Blob
A cheaper, short-lived type of data that rollups post to Ethereum, added by EIP-4844. Source