Reading the chain: key words

A website that searches a blockchain's public records and shows transactions, addresses, blocks and tokens in readable form. It can't change the chain. Source

A unique code for one transaction, used to look it up. Also called a transaction ID or txid. Source

A count of how far a transaction is buried. Each new block on top adds one. More confirmations make a transaction safer to rely on. Source

The exact units of gas a transaction used. An explorer multiplies it by the gas price to show the fee. Source

The price actually paid per unit of gas: the base fee plus the tip. Source

Extra data sent with a transaction, most often the function call for a smart contract. Source

The first 4 bytes of the input data. They pick which contract function to run. Also called the function selector. Source

A record a smart contract writes while it runs, for apps outside the chain to read. Explorers show logs on a Logs tab. Source

The log an ERC-20 token contract must write whenever tokens move. It holds from, to and value. Source

ETH moved by a smart contract as part of a transaction someone else started. Source

A token setting that says where the decimal point goes. Divide the raw number by 10 to the power of decimals to get the amount people see. Source

A name an explorer shows next to an address. It comes from the explorer, not from the chain. Source

A contract whose source code an explorer has checked compiles to the code on the chain. It does not mean the contract is safe. Source

Permission you give an app to spend your tokens. Explorers can list approvals and help you revoke them. Source

An unspent transaction output: an amount of bitcoin waiting to be spent by a later input. Source

An output that sends the leftover of a Bitcoin payment back to the sender. Source