Sequencer
A sequencer is a system in a Layer 2 network that orders user transactions and batches them before they are submitted to the base blockchain.
In crypto, a sequencer is most often associated with Layer 2 networks such as rollups. It receives transactions from users, decides their order, and groups them into batches that are later posted to a base chain like Ethereum. This helps the Layer 2 give users fast transaction confirmations without waiting for every transaction to be individually processed on the main chain.
Sequencers matter because transaction ordering affects speed, costs, and fairness. A well-run sequencer can make a Layer 2 feel quick and inexpensive, while a centralized or poorly designed one can create risks such as downtime, censorship, or unfair ordering. For example, using a rollup with a sequencer is a bit like joining a checkout line managed by one cashier who organizes many purchases before sending the final receipt to the main accounting system. Some Layer 2 projects aim to decentralize sequencing over time so no single operator controls the ordering process.
Other terms in Layer 2 & Scaling
Data Availability
The assurance that the transaction data needed to verify a blockchain or layer 2 network can be accessed by anyone who needs it.
Fraud Proof
A fraud proof is evidence submitted to a blockchain to show that a proposed transaction result or rollup state is invalid.
Layer 2
A Layer 2 is a secondary network or protocol built on top of a blockchain to process transactions faster and cheaper while relying on the main chain for security.
Layer 3
A Layer 3 is an application-specific blockchain layer built on top of a Layer 2 to add customization, scalability, or specialized features.