There is a lot of terminology surrounding Polkadot and the blockchain in general. In this article we try to cover the most basic terms that you may come across in articles, videos or your communication with us. 

Some of these terms have variances, meaning different resources use slightly different names for the same thing, and we mention these too, so you know what is being referred to in all cases.

Finally, the definitions given here have been simplified somewhat. For the precise technical definitions, and the full Polkadot glossary, check the Wiki Glossary.

Polkadot-JS UI

The user interface at https://polkadot.js.org/apps/ that can be used as a wallet for your accounts on all Substrate chains, a block explorer, to issue extrinsics directly, query the chain, check on governance proposals and so much more. It provides the full functionality Polkadot and Substrate chains in general have to offer.

a.k.a. (also known as)

• polkadot.js (technically this refers to the collection of JavaScript tools for Polkadot that the UI is built upon)
• polkadot.js.org
• Polkadot-JS Apps UI (official term)

Polkadot extension

By this term we refer to the browser extension available for Chromium based browsers (Chrome, Brave, Edge) and Firefox. The extension allows the management of accounts and interaction with any site and dApp that is built on Substrate. It's a gateway to the wider Polkadot ecosystem.

However, you cannot send funds, or take other actions, directly from the extension. For this the extension needs to interact with a UI, like the Polkadot-JS UI.

a.k.a.

• Polkadot-JS extension
• Polkadot {js} browser plugin or extension (official term)
• Polkadot browser extension

Mnemonic phrase

The mnemonic phrase of your account is the list of 12 words that you are given whenever you create a new account. These words can restore your account in case you lose access to it. 

This is an industry standard that all non-custodial wallets adopt, although a mnemonic phrase generated in one wallet won't necessarily produce the same account on another, at least not without additional information. Also, some wallets, like Ledger, use 24 words instead of 12.

The mnemonic phrase is the "key to the kingdom". It gives full access to your account, which is why you should never share it with anyone and keep it only on paper, in a safe and secret location. You can learn more about protecting yourself from scams and hacks here.

a.k.a.

• Mnemonic seed
  
• Seed (official term)
• 12-word phrase
• Recovery phrase

Private key

The private key is a hexadecimal number that is used to sign extrinsics. It's the private counterpart of the private-public key pair and as the name suggests it needs to be kept safe and secret, because it's the only thing needed to prove ownership over an account. It's derived from the mnemonic phrase (along with the public key) but unlike the mnemonic phrase you'll seldom encounter it or interact directly with it.

a.k.a.

• Raw seed (official term)
  

Public key

The public key is the low-level representation of your account. It's a hexadecimal number and the public counterpart of the private-public key pair. This means that it can safely be shared as it doesn't give access to your account. However, you'll almost never have to use it directly. Instead, in almost all cases you'll interact with your account's address. That's what you'll use to have funds sent to your account.

Account

Your account is where your tokens are stored. These tokens can be DOT, KSM or any other token on a Substrate chain, because an account can be used on almost all chains built on Substrate. You can read more about that here. 

On low-level it's represented by your public key, but each chain has its own address format and the address on each chain is what you use to receive funds in your account on that chain. That's why the terms account and account's address (or simply address) actually refer to two different things. You can learn more about Substrate accounts and the various address formats in this video.

Substrate

We keep referring to Substrate chains and accounts and address format, but what is Substrate? Substrate is a blockchain framework. It's basically a set of tools that can be used and customised to create new blockchains easily. Polkadot, Kusama and all other chains, parachains and testnets that are included in Polkadot-JS UI are built on Substrate.

Generic Substrate address

The generic Substrate address refers to an address format that starts with 5 and isn't the address format of any specific chain (although some chains use this format as their native address format), but rather a generic representation of an account that theoretically represents the account on all chains. 

a.k.a.

• Substrate address
• Substrate address format
• Substrate account (technically this means an account that can be used on Substrate chains)

NOTE: We've bolded theoretically, because although you can use the Substrate address to send DOT, KSM or any other token to your account, and it would "land" in the correct chain, most wallets and exchanges don't support this and they send only to the specific address format of the respective chain. 

Extrinsic

The extrinsic is a piece of information from the outside world that changes the state of the blockchain. The most common example of an extrinsic is the transfer extrinsic that sends tokens from one account to another. 

This fundamental extrinsic would be called a transaction on other blockchains, like Bitcoin, but extrinsics are so much more and there are a lot of them that do a lot of other things besides transferring balance, like bonding and unbonding, nominating, voting on governance and even updating the chain itself!

An extrinsic is identified uniquely by its ID, which is the block number followed by the index of the extrinsic in that block, for example 6953825-1.

a.k.a.

• Transaction

NOTE: The extrinsic hash is not a unique identifier. You can read more about this here.

Protocol

This is a quite broad term that refers to the rules of the chain, be it Polkadot, Kusama or another Substrate chain. Or to put it differently, how the chain works and what happens in each case. This is what ensures the result of an extrinsic is deterministic.

a.k.a.

• Runtime (official term)

Chilling

An account chills when it stops nominating or validating. The chilling could be voluntary or it could be forced. A case where a nominator may be chilled is if they are below the minimum stake needed to validate and someone calls the "chill_other" extrinsic. A validator may be chilled if they are offline for a prolonged period of time (at least 12 hours on Polkadot).

NOTE: Chilling doesn't unbond your tokens. It simply signals the intention to stop nominating or validating.

Account reaped

An account is reaped when its balance drops below the existential deposit (ED). When that happens any remaining balance in the account is burned (lost forever) and the account is deactivated. To reactivate a reaped account you need to send to it at least the ED.

a.k.a.

• Account deactivated

Bonding and Staking

These terms are usually used interchangeably, but they mean slightly different things. Bonding is the action of locking up your tokens and this is usually done in order to stake with them. Staking is using these locked tokens to participate in the security of the network either by validating or nominating validators.

The reverse actions are called unbonding and unstaking, although that second term is not really used. We call that action "chilling" and as mentioned above, chilling doesn't also unbond your tokens. 

NOTE: Unbonding takes 28 days on Polkadot and 7 days on Kusama.