> ## Documentation Index > Fetch the complete documentation index at: https://docs.sqd.dev/llms.txt > Use this file to discover all available pages before exploring further. # SQD Glossary > Definitions of key terms used across SQD documentation — archives, gateways, workers, Portals, squids, processors, slots, tags, and more. ### `Archives` Deprecated term used for [SQD Network](/en/network/overview) and for the data sourcing service of the deprecated FireSquid SDK version. Occasionally refers to a chain-specific endpoint available from either source (e.g. "an Ethereum archive"). The new terminology is: * "Archives" as an abstract collection of services for some networks is replaced by "[SQD Network](/en/network/overview)" (when referring to data location) or "SQD Network gateway" (when referring to the service) * "public Archives" are replaced by the [open private version](/en/network/overview) of SQD Network * "an archive" for a particular network is replaced by "a SQD Network gateway" List of gateways for the open private SQD Network is available in the [EVM](/en/data/evm), [Substrate](/en/data/substrate), [Solana](/en/data/solana), and [Other](/en/data/other) listings, and via [`sqd gateways`](/en/cloud/reference/cli/gateways). **Not to be confused with [archive blockchain nodes](https://ethereum.org/developers/docs/nodes-and-clients/archive-nodes)**. ### `archive-registry` The deprecated NPM package `@subsquid/archive-registry` that was used to look up squid data sources by network aliases (with `lookupArchive()` and a small CLI). We now recommend using raw gateway URLs instead of `lookupArchive()` calls in processor configuration. The exploratory CLI is replaced by [`sqd gateways`](/en/cloud/reference/cli/gateways); per-chain gateway listings are available under the [EVM](/en/data/evm), [Substrate](/en/data/substrate), [Solana](/en/data/solana), and [Other](/en/data/other) sections. ### `Block` An atomic state transition of a blockchain. Typically an ordered collection of transactions. ### `Call` On [Substrate](#substrate), a call is a sub-routine changing the runtime state. An extrinsic consists of a root call which in turn may have sub-calls, thus calls executed by an extrinsic have parent-child relationship. For example, `util.batch` extrinsic has a single root call and multiple child calls. SQD processor is call-based rather than extrinsic based, as normally one is interested in specific calls changing the substrate state, no matter if it was part of a batch extrinsic, or it was wrapped in a sudo or proxy call. ### `Cloud (former Aquarium)`") A [cloud service](/en/cloud/) for deploying [squids](#squid) in a serverless fashion maintained by Subsquid Labs GmbH. ### `Contracts pallet` [`Contracts`](https://substrate-developer-hub.github.io/substrate-how-to-guides/docs/pallet-design/add-contracts-pallet/) is a [pallet](#pallet) developed by Parity to execute WASM-based smart contracts. ### `ETL` Stands for Extract-Transform-Load. A pipeline to extract data from the source, enrich, transform, normalize and load into the target data store. ### `Event` An operation performed during a blockchain state transition that results in emission of a structured log message. Subsequently, the message can be retrieved from blockchain nodes. ### `EVM` Stands for the Ethereum Virtual Machine. An instruction set and the runtime specification originally developed for the Ethereum network which was later adopted by many other chains (e.g. BSC, Polygon). ### `Extrinsic` On [Substrate](#substrate), a generalized transaction externally submitted to a Substrate runtime for execution. There are [technical nuances](https://substrate.stackexchange.com/questions/2248/is-a-transaction-an-extrinsic) differentiating transactions and extrinsics. ### `FRAME pallets` A collection of standard [Substrate](#substrate) pallets maintained by Parity. Currently kept in the [Substrate Repo](https://github.com/paritytech/substrate/tree/master/frame). ### `Frontier pallet` [Frontier](https://github.com/polkadot-evm/frontier) is a [Substrate](#substrate) [pallet](#pallet) implementing the [Ethereum Virtual Machine](#evm). In particular, Substrate chains with Frontier pallet support EVM-based smart contracts. ### `GraphQL` A declarative query language and an API specification language developed by Facebook as an alternative to REST. See the official [GraphQL docs](https://graphql.org/) for more details. ### `Hot blocks` An alternative term for [unfinalized blocks](/en/sdk/squid-sdk/resources/unfinalized-blocks) that emphasizes the fact that the data extracted from these blocks is volatile. Sometimes used in Squid SDK code and comments. ### `ink!` An SDK (software development kit) and a smart-contract language for developing WASM-based smart contracts, maintained by Parity. The contracts developed with ink! are compiled into a WASM blob compatible with the API exposed by the [`Contracts` pallet](#contracts-pallet). More details [here](https://use.ink). ### `OpenReader` 1. SQD's own open source [GraphQL server](/en/sdk/squid-sdk/reference/openreader-server/overview), built in-house. No longer recommended for new projects running PostgreSQL due to its [limitations](/en/sdk/squid-sdk/reference/openreader-server/overview#limitations). See [Serving GraphQL](/en/sdk/squid-sdk/resources/serving-graphql) to learn more. 2. The GraphQL [schema generation library](https://github.com/subsquid/squid-sdk/tree/master/graphql/openreader) at the heart of 1. Implements [OpenCRUD](https://www.opencrud.org/). ### `Pallet` A portable module that can be added to a [Substrate](#substrate) runtime. Typically, contains a self-contained implementation of a business logic that can be re-used across multiple chains. ### `Schema file` A file describing the target data schema for a squid, normally called `schema.graphql`. The file uses a GraphQL dialect to define entities, properties and relations. See [details here](/en/sdk/squid-sdk/reference/schema-file). ### `State` A key-value map defining the internal worldview of an EVM contract of a Substrate runtime at a specific point in time. The consensus algorithm ensures that the honest majority of the nodes agree on the runtime state. ### `Storage` On [Substrate](#substrate), a persistent key-value database kept by the chain nodes. It is used to access the current and historical [state](#state). See details on the [Substrate docs page](https://docs.substrate.io/fundamentals/state-transitions-and-storage/) ### `Squid` A project consisting of an [ETL](#etl) for extracting and transforming on-chain data (squid processor), and optionally an API to present the data (squid API). ### `Squid processor` The [ETL](#etl) part of the squid. Extracts on-chain data from an [SQD Network](/en/network/overview) gateway and/or directly from chain RPC, then transforms and optionally enriches it with external data. Saves the result into a target [data sink](/en/sdk/squid-sdk/reference/store). ### `Squid API` The data presentation part of the squid. Typically, it's an [OpenReader](#openreader) GraphQL API auto-generated from a schema file. ### `Substrate` [Substrate](https://substrate.io) is a framework for developing blockchain runtimes. Used to develop the Polkadot, Kusama chains and all the parachains. ### `Substrate Runtime` The code that defines the state transition logic of a blockchain, and by extention its business logic. See details on the [Substrate docs page](https://docs.substrate.io/fundamentals/architecture/). ### `Squid SDK` [Squid SDK](/en/sdk/squid-sdk/overview) is a collection of open-source libraries for building [squids](#squid). ### `Typegen` A tool generating strongly typed data access classes from a metadata in some format. Squid SDK includes typegen tools: * for accessing EVM smart contract data based on the contract ABI * for accessing event, extrinsics and storage data based on [Substrate](#substrate) metadata * for accessing [ink!](#ink) smart contract data based on the contract metadata See [this section](/en/sdk/squid-sdk/resources/tools/typegen/generation) for documentation on these tools. ### `WASM` A portable binary code format and an execution environment specification. WASM programs enjoy deterministic outputs and near-native execution speeds, which makes WASM an attractive alternative to EVM. [Edit this page](https://github.com/subsquid/docs/edit/master/docs/glossary.md)