Add missing glossary to ref docs (#2572)

This PR is the same as
https://github.com/paritytech/polkadot-sdk/pull/2273, but that one had
too many conflicts after a base change. As it is a just one file PR I
decided to start over with a clean slate.

---
This PR adds some missing glossary definitions to the Developer Hub ref
docs

FIxes https://github.com/paritytech/polkadot-sdk-docs/issues/40

developer-hub/src/reference_docs/glossary.rs

@@ -36,27 +36,85 @@
 //!
 //! #### Offchain
 //!
-//! #### Host Function:
+//! Refers to operations conducted outside the blockchain's consensus mechanism. They are essential
+//! for enhancing scalability and efficiency, enabling activities like data fetching and computation
+//! without bloating the blockchain state.
+//!
+//! #### Host Functions:
+//!
+//! Host functions are the node's API, these are functions provided by the runtime environment (the
+//! [host](#host)) to the Wasm runtime. These functions allow the Wasm code to interact with and
+//! perform operations on the [node](#node), like accessing the blockchain state.
 //!
 //! #### Runtime API:
 //!
+//! This is the API of the runtime, it acts as a communication bridge between the runtime and the
+//! node, serving as the exposed interface that facilitates their interactions.
+//!
 //! #### Dispatchable:
 //!
-//! Callable
+//! Dispatchables are [function objects](https://en.wikipedia.org/wiki/Function_object) that act as
+//! the entry points in [FRAME](frame) pallets. They can be called by internal or external entities
+//! to interact with the blockchain's state. They are a core aspect of the runtime logic, handling
+//! transactions and other state-changing operations.
+//!
+//! **Synonyms**: Callable
 //!
 //! #### Extrinsic
 //!
+//! An extrinsic is a general term for a piece of data that is originated outside of the runtime,
+//! included into a block and leads to some action. This includes user-initiated transactions as
+//! well as inherents which are placed into the block by the block-builder.
 //!
 //! #### Pallet
 //!
+//! Similar to software modules in traditional programming, [FRAME](frame) pallets in Substrate are
+//! modular components that encapsulate distinct functionalities or business logic. Just as
+//! libraries or modules are used to build and extend the capabilities of a software application,
+//! pallets are the foundational building blocks for constructing a blockchain's runtime with frame.
+//! They enable the creation of customizable and upgradeable networks, offering a composable
+//! framework for a Substrate-based blockchain. Each pallet can be thought of as a plug-and-play
+//! module, enhancing the blockchain's functionality in a cohesive and integrated manner.
+//!
 //! #### Full Node
 //!
+//! It is a node that prunes historical states, keeping only recent finalized block states to reduce
+//! storage needs. Full nodes provide current chain state access and allow direct submission and
+//! validation of extrinsics, maintaining network decentralization.
+//!
 //! #### Archive Node
 //!
+//! An archive node is a specialized node that maintains a complete history of all block states and
+//! transactions. Unlike a full node, it does not prune historical data, ensuring full access to the
+//! entire blockchain history. This makes it essential for detailed blockchain analysis and
+//! historical queries, but requires significantly more storage capacity.
+//!
 //! #### Validator
 //!
+//! A validator is a node that participates in the consensus mechanism of the network.
+//! Its role includes block production, transaction validation, network integrity and security
+//! maintenance.
+//!
 //! #### Collator
 //!
+//! A collator is a node that is responsible for producing candidate blocks for the validators.
+//! Collators are similar to validators on any other blockchain but, they do not need to provide
+//! security guarantees as the Relay Chain handles this.
+//!
 //! #### Parachain
 //!
-//! aka. AppChain.
+//! Short for "parallelized chain" a parachain is a specialized blockchain that runs in parallel to
+//! the Relay Chain (Polkadot, Kusama, etc.), benefiting from the shared security and
+//! interoperability features of it.
+//!
+//! **Synonyms**: AppChain
+//!
+//! #### PVF
+//! The Parachain Validation Function (PVF) is the current runtime Wasm for a parachain that is
+//! stored on the Relay chain. It is an essential component in the Polkadot ecosystem, encapsulating
+//! the validation logic for each parachain. The PVF is executed by validators to verify the
+//! correctness of parachain blocks. This is critical for ensuring that each block follows the logic
+//! set by its respective parachain, thus maintaining the integrity and security of the entire
+//! network.
+//!
+//! **Synonyms**: Parachain Validation Function