Common Crypto Terms

A consensus attack where a single entity controls more than 50% of the network's hash rate (PoW) or stake (PoS). This allows them to censor transactions and double-spend coins by reorganizing the chain, but NOT to steal other people's funds or change protocol rules.

Application Binary Interface. The standard JSON format that describes how to encode and decode data to call a smart contract's functions.

A hexadecimal identifier (e.g., `0xabc...`) derived from the public key. An Externally Owned Account (EOA) is controlled by a private key, whereas a Contract Account is code.

The finite capacity of a blockchain to record data. Because blocks are produced on a fixed schedule with a gas limit, blockspace is a scarce resource that users bid for via gas fees.

A protocol that connects independent blockchains. Most work via 'Lock and Mint': you lock assets on Chain A, and the bridge mints a wrapped representation on Chain B.

Low-level machine code executed by the EVM. Smart contracts are written in high-level languages (Solidity) but compiled into bytecode for the network to execute.

A 'Transaction' writes data to the blockchain, costs gas, and requires a signature. A 'Call' reads data from a local node, costs zero gas, and does not broadcast anything.

A read-only, non-persistent area where function arguments are stored during a transaction execution. Cheaper than using storage memory.

The assurance that a block cannot be altered or reversed without burning a significant amount of economic value. In Bitcoin, finality is probabilistic. In Ethereum PoS, it is deterministic.

A divergence in the blockchain's protocol rules. 'Soft Forks' are backward-compatible upgrades. 'Hard Forks' are incompatible and require all nodes to upgrade.

The unit of computational work. 'Gas Limit' is how much work you allow. 'Gas Price' is how much you pay per unit. Total Fee = Gas Used × Gas Price.

A cryptographic algorithm (like Keccak-256) that maps data of arbitrary size to a fixed-size bit string. It is deterministic and collision-resistant.

The waiting area for transactions that have been broadcast but not yet included in a block. Validators select transactions from here to build the next block.

Maximal Extractable Value. The profit a validator can make by including, excluding, or reordering transactions within a block (e.g., arbitrage, sandwich attacks).

A counter associated with an address. It increments with every transaction to enforce ordering and prevent replay attacks.

Operational Code. The lowest-level instruction the EVM understands (e.g., `PUSH`, `POP`, `SSTORE`). Each opcode has a specific gas cost.

A Layer 2 scaling solution that assumes transactions are valid by default. It allows a challenge period (usually 7 days) where anyone can submit a Fraud Proof to dispute invalid state.

A bridge between the blockchain and the outside world. Oracles fetch off-chain data (prices, weather) and post it on-chain for smart contracts to use.

A 256-bit number generated from entropy. It allows you to sign transactions, mathematically proving ownership of an address without revealing the key itself.

A vulnerability where a malicious contract calls back into the calling contract before the first execution is finished, often draining funds if state isn't updated first.

Chain Reorganization. When a node switches its canonical chain to a longer/heavier version received from the network. Discarded blocks become 'uncle' blocks.

A scaling technology that executes transactions outside the main chain (L2) but posts transaction data to the main chain (L1), inheriting its security.

A human-readable representation (12-24 words) of the master entropy that generates your wallet's private keys (BIP-39 standard).

A cryptographic proof produced by signing a transaction hash with a private key. It proves authorization without revealing the key.

The mechanism in Proof-of-Stake where a validator loses a portion of their staked ETH for malicious behavior, such as double-signing blocks.

Immutable code deployed to a blockchain address. It runs deterministically on the EVM according to its logic.

The Merkle Root of the entire state (balances, storage, etc.) at a specific block height. Light clients verify this instead of downloading the full state.

An attack where a single adversary controls many fake identities to gain disproportionate influence. PoW (Energy) and PoS (Capital) are defenses.

A method to prove a statement is true without revealing valid information beyond the statement itself (e.g., proving you are an adult without showing your DOB).

A Layer 2 scaling solution that uses Zero-Knowledge Validity Proofs to instantly prove the correctness of off-chain computation.