What is a token? (BTC, ERC-20, SPL)
A native coin is built into the network; a token is issued on top of it. A standard is the quiet hero that lets a new asset plug in on day one.
The word "token" gets used for everything, which buries an important distinction. Some assets are a blockchain's native unit, and some are issued on top of a blockchain.
Native coins vs. tokens
A native coin is the built-in asset of a network (BTC on Bitcoin, ETH on Ethereum, SOL on Solana). It's woven into the protocol: it pays gas fees and, on Proof of Stake chains, it's what validators stake to secure the network.
A token (in the stricter sense) is created on an existing chain by a smart contract, without launching a new network. Ethereum's ERC-20 standard, proposed by Fabian Vogelsteller in 2015, is the most famous: a shared set of rules (check a balance, transfer, approve a spender) any project can implement to mint a fungible token. Because every ERC-20 follows the same interface, every wallet and exchange supports a new one instantly. Solana's equivalent is the SPL token standard. The labels simply tell you which chain a token lives on and which rulebook it follows.
Fungible vs. non-fungible
The other axis is fungible vs. non-fungible. Fungible tokens are interchangeable — one USDC is as good as any other. Non-fungible tokens (NFTs), Ethereum's ERC-721 standard (proposed by William Entriken and co-authors in 2018), are each unique and individually identifiable, which lets them represent a specific item: art, a membership, a deed.
The standard is the quiet hero
A standard is an agreed interface — a promise about what functions a contract exposes. That shared promise is why the ecosystem composes: a new token plugs into existing wallets, exchanges, and apps on day one, with no permission required ("money Lego").
The flip side: anyone can mint a token and name it anything. A token labeled "USDC" or "ETH" in your wallet may be a worthless impostor. Legitimacy comes from the contract address and issuer — so verify the contract.
Why it matters. A token standard is permissionless issuance in action. In the old world, creating a financial instrument means lawyers, licenses, and gatekeepers. On an open chain, issuing an asset is a few lines of code anyone can deploy. The danger (scams) and the promise (open access, composability) are two faces of the same permissionless coin.