What is Blockchain?

A blockchain is a ledger that many computers keep identical copies of, appended in batches called blocks, where each block references the previous one so that history cannot be rewritten quietly. The interesting property is not the chain of blocks but the agreement: thousands of independent machines converge on the same record without a central operator, using a consensus rule such as proof of work or proof of stake.

What goes in the ledger depends on the chain. Bitcoin records transfers of one asset. Ethereum and its relatives record transfers and the state of smart contracts, which is why a single Ethereum block can move tokens, settle trades and mint NFTs. Solana, TON and Tron make different trade-offs between speed, cost and decentralization, and each is its own ledger with its own addresses.

Public means public. Every balance, every transfer and every contract interaction on a public chain can be read by anyone, forever. Privacy comes from not linking an address to a person, not from the data being hidden. This is the property that makes read-only portfolio tracking possible at all: an address is enough to see everything it holds.

The practical consequence for a holder is that assets live on chains, not in apps. Closing an exchange account or deleting a wallet app changes nothing on the chain. TrueHold reads chains directly by address, so the view of a wallet depends on the ledger, not on any service staying in business.

Block explorers are the windows onto a chain: paste an address or a transaction hash and see the raw record. Every chain has one, from Etherscan to Solscan, and they are the reference when a wallet, an exchange and a tracker disagree. Learning to read one takes an evening and removes most of the mystery from what a portfolio tool shows you.