> ## Documentation Index
> Fetch the complete documentation index at: https://docs.polygon.technology/llms.txt
> Use this file to discover all available pages before exploring further.

# Glossary

> Definitions of technical terms used throughout the Polygon CDK documentation.

### Agglayer

Agglayer is a cross-chain settlement layer that connects the liquidity and users of any blockchain for fast, low-cost interoperability and growth. It enables trustless bridging, shared messaging, and unified state across Layer 2s using zero-knowledge (ZK) proofs.

[Visit agglayer.dev](https://www.agglayer.dev/)

### Polygon CDK (Chain Development Kit)

An enterprise-grade toolkit for building custom Ethereum Layer 2 chains. Each CDK chain is natively connected to Agglayer for cross-chain interoperability, shared liquidity, and integrated messaging. CDK supports **op-geth** and **op-reth** execution clients.

### Chain Operator

An individual, team, or DAO responsible for launching and managing a CDK-based chain. Operators may handle sequencing, bridge operations, infrastructure deployment, data availability configuration, and other network responsibilities.

### Data Availability (DA)

The requirement that transaction data remains accessible to Layer 1 validators for verifying off-chain execution. DA ensures the security of modular rollups. CDK chains can use onchain DA (e.g., Ethereum), off-chain DACs, or local solutions.

### Data Availability Committee (DAC)

A decentralized set of nodes that ensures off-chain data availability for CDK chains using Validium mode. DAC nodes fetch transaction data, verify it, sign it, and store it for later retrieval.

### Implementation Providers (IPs)

External infrastructure teams that assist developers with launching and maintaining CDK chains. Conduit and Gateway both support op-reth and op-geth execution clients and are building open source tooling for CDK deployments.

### Rollups

Layer 2 solutions that execute transactions off-chain and post state data to Ethereum. CDK supports multiple rollup types, including:

* [Optimistic rollups](https://ethereum.org/en/developers/docs/scaling/optimistic-rollups/)
* [ZK rollups](https://ethereum.org/en/developers/docs/scaling/zk-rollups/)
* Validium (ZK with off-chain DA)
* Sovereign (non-ZK with pessimistic proofs)

### Sovereign Mode

A rollup configuration that does not use a ZK prover. Instead, Agglayer enforces security through pessimistic proofs, ensuring that no chain can withdraw more than it deposits. Default configuration for CDK chains.

### Unified Bridge

The shared bridge infrastructure for CDK chains, providing secure cross-chain asset transfers and messaging. It supports shared escrow, sovereign and ZK rollup flows, and native Agglayer integration.

### Unified Escrow

A component of the Unified Bridge that holds tokens either bridged from Ethereum or minted natively on Layer 2. Ensures consistent accounting and solvency across all CDK chains.

### Validium

A rollup configuration that uses ZK proofs for execution but stores transaction data off-chain, reducing costs and increasing throughput. CDK Validium chains rely on DACs for off-chain data availability.

[Learn more about Validium](https://ethereum.org/en/developers/docs/scaling/validium/)

### ZK Proofs

Zero-knowledge proofs validate computations without revealing input data. Agglayer uses ZK proofs to provide cryptographic guarantees for execution, enabling fast finality and trustless security across chains.