# Terms

In this documentation, we introduce some new terms:

### MetaID

MetaID is defined as the root index value of the user data tree. This value is globally unique. The MetaID protocol is essentially a set of conventions for generating this user data tree. In this document, MetaID sometimes refers to this index value, and sometimes the MetaID protocol and related methods are simply referred to as MetaID.

#### Generation Rules

The generation rule of MetaID is based on processing the user's Address through SHA256 hash, so the Address itself has a unique MetaID.

```
MetaID = SHA256(Address)
```

#### MetaID Tree

The tree-structured data generated according to MetaID rules is called a "MetaID Tree". The MetaID Tree is constructed through the path in the user's own PIN, forming an interconnected, DAG-structured data. See the "[MetaID Tree Introduction](/metaid-specification/metaid-tree/metaid-tree.md)" entry for details.

### PIN

PIN stands for Personal Information Node. Each node and leaf on the MetaID Tree is a PIN. In simple terms, every piece of MetaID data inscribed on the chain is called a PIN. See the "[About PIN"](/metaid-specification/about-pin.md) entry for details.

### PoP

PoP stands for Proof of PIN. It is related to randomness and the hashrate difficulty of the block where the PIN is located. PoP is used to reflect the value of the user's MetaID data and the user's "workload" in the MetaID world. See the "[About PoP](/metaid-specification/about-pop.md)" entry for details.

### MAN

MAN stands for MetaID App Node. It is the first backend indexer that follows the MetaID V2 protocol, aiming to create a distributed storage node based on MetaID and facilitate developers to develop decentralized MetaID applications without relying on third-party service providers. See the relevant documents in the "[MAN introduction](/metaid-app-node/introduction.md)" section for details.

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