Blockchain & Web3 Vocabulary

Immutability means that once a block of data is added to the chain, altering it requires recomputing the cryptographic hash of that block and all blocks that follow — computationally infeasible on a large network. This is enforced by linking blocks: each block contains the hash of the previous block, so changing any historical record breaks the chain. The four foundational blockchain properties: Immutability — records cannot be changed retroactively. Decentralisation (option A) — no single entity controls the ledger; thousands of nodes hold copies. Transparency (option C) — on public blockchains (Bitcoin, Ethereum), all transactions are publicly visible (though pseudonymous). Consensus (option D) — a mechanism (PoW, PoS) by which nodes agree on the valid state before committing a block. Together, these properties make blockchain useful for: supply chain provenance, digital ownership (NFTs), financial settlement, and public audit trails. In conversation: "The immutability of the blockchain record is what clients in our supply chain use to verify the authenticity of components."

A smart contract is a self-executing program stored on a blockchain that automatically enforces and executes agreed-upon rules when predefined conditions are met — with no need for a trusted third party. Properties: Deterministic — same inputs always produce same outputs on every node. Immutable once deployed — code cannot be changed (upgradeable patterns exist but are complex). Transparent — source code is publicly auditable on-chain. Trustless — execution is enforced by the network, not a company. Written in Solidity (Ethereum), Rust (Solana, Near), or Vyper (Ethereum alternative). Other terms: dApp (decentralised application) (option A) — a full application whose backend logic runs on smart contracts. The frontend is still a regular web app. Consensus node (option C) — a network participant that validates transactions; not the business logic itself. Oracle (option D) — a service that feeds real-world data (price feeds, event results) to a smart contract, which can't access external data on its own (Chainlink is the most common oracle network). In conversation: "The escrow logic is in a smart contract — funds are released automatically when the delivery condition is confirmed on-chain."

A crypto wallet like MetaMask is software that manages your private key and lets you interact with blockchain networks. It doesn't actually store tokens — tokens exist on-chain; the wallet controls the key that proves ownership. Signing a transaction is the cryptographic act of: (1) taking the transaction data (to: address, value, gas), (2) hashing it, (3) encrypting it with your private key → producing a digital signature. The network verifies this with your public key / wallet address, confirming you authorised the transaction without ever seeing your private key. Key vocabulary: Private key — a 256-bit secret that proves ownership; must never be shared. Public key / address — derived from your private key; can be shared publicly (like an account number). Seed phrase / recovery phrase — 12–24 words that derive all your keys; backing this up is critical. Cold wallet / hardware wallet (Ledger, Trezor) — keys stored on offline hardware for security. Hot wallet — keys online (MetaMask, Coinbase Wallet) — convenient but more vulnerable. In conversation: "We never handle users' private keys — all transaction signing happens client-side in their wallet."

Gas is Ethereum's unit of computational cost. Every operation in the EVM (Ethereum Virtual Machine) — storing data, running arithmetic, emitting events — has a fixed gas cost. The total gas used × the gas price (in gwei, a fraction of ETH) = the transaction fee paid to validators. Why gas exists: it prevents infinite loops and spam — each computation costs real money, making attacks expensive. Gas vocabulary: Gas limit — the maximum gas the sender will pay (set by the user). Gas price / base fee + priority fee — cost per unit of gas (EIP-1559 model). Gas fee — total cost = gas used × price. Gwei — 1 ETH = 10⁹ gwei; gas prices are quoted in gwei. Out-of-gas error — transaction fails if it runs out of gas before completing. Layer 2 scaling solutions (Optimism, Arbitrum, zkSync) reduce gas costs by batching transactions off-chain. DeFi (Decentralised Finance) in the question: protocols that replicate financial services (lending, trading, yield farming) using smart contracts without banks. The gas cost problem is a major DeFi UX challenge. In conversation: "High gas fees make microtransactions impractical on L1 — we're migrating to an L2 rollup."

NFT = Non-Fungible Token. Fungible means interchangeable — one ETH is worth exactly the same as any other ETH. Non-fungible means each token has unique properties and cannot be replaced by another token of the same type. NFT standards: ERC-721 — the original Ethereum NFT standard; each token ID is unique. ERC-1155 — supports both fungible and non-fungible tokens in one contract (gaming items). Use cases beyond art: Digital collectibles / art — CryptoPunks, Bored Apes. Gaming assets — in-game items with verifiable on-chain ownership. Event tickets — counterfeit-proof entry tokens. Domain names — ENS (.eth) names. Real-world asset tokenisation — real estate, certificates, IP rights. Common misconceptions: Owning an NFT proves on-chain ownership of a token ID — not legal copyright to the underlying content (unless the licence explicitly grants it). The image is usually stored off-chain (IPFS, Arweave) — only the ownership record is on-chain. In conversation: "The NFT gives holders provable on-chain ownership of their membership — they can transfer or sell it without our platform's involvement."

Immutability refers to the fundamental property of blockchains – once data is written to a block, it's extremely difficult (practically impossible without consensus) to change. Option A describes mutable behavior, which is the opposite of what's intended. Options B and D misrepresent how blockchain consensus works; immutability isn't about automatic correction or universal agreement, but rather resistance to alteration.

'Out of Gas' isn't a problem with your wallet or the compiler; it indicates that the transaction consumed more gas than was initially provided. Ethereum uses 'gas' as a unit to measure computational effort—if a transaction requires more computation than expected (often due to complex logic or high network congestion), the execution halts, and the transaction fails. Options A, C, and D are related issues but don't directly explain the 'out of gas' error.

While smart contracts *can* handle royalty management (option D), their primary role in this scenario is to provide a permanent, tamper-proof record of the NFT's metadata and its associated ownership information on the blockchain. The contract acts as the digital certificate of authenticity and proof of provenance, ensuring that the NFT's identity remains consistent across the network. Options A and B are not functions of smart contracts.

When David says 'querying the blockchain directly,' he means accessing the underlying Ethereum network itself – typically through tools like `eth_` RPC calls – to retrieve data from blocks and smart contracts. This bypasses any intermediary API layers, which can introduce latency. Options B, C, and D represent alternative solutions for improving data access, but don't describe direct blockchain querying.

The smart contract's role isn't simply to store or trade tokens (options A, C, and D). Instead, it executes the core logic of the game's economic rules – verifying player actions (e.g., completing a quest) and automatically distributing tokens based on those actions. This automation removes the need for intermediaries and ensures transparency in the token economy.