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You already know that money never appears or vanishes. It moves from a source to a destination, and both sides get recorded. Now for the movement itself: what one complete movement is, the names of its pieces, and where the money sits before a movement finishes. Picture handing cash across a counter. The moment the cash leaves your hand and lands in the other person’s, the whole exchange happened as one event. A banking system treats movement the same way: one complete handover, recorded in full, all at once.

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One movement, recorded in full

A transaction is one complete movement of value: the whole event, start to finish. When a customer sends R$100 to a merchant, that single transaction is the R$100 changing hands. But you’ve already seen that every movement has two sides. So a transaction has smaller pieces:
  • An operation is one part of the movement: a single debit or a single credit.
  • A transaction consists of operations that balance: everything debited equals everything credited.
The R$100 transfer is one transaction with two operations. One is a debit of R$100 that leaves the customer. The other is a credit of R$100 that arrives at the merchant. Same amount, opposite directions, recorded together.
An operation is one part of a movement. A transaction is the whole movement. The operations are its parts.

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The shapes a movement can take

The simplest movement has one source and one destination, but a single transaction can spread across more accounts. However many parts it has, it always balances. The common shapes:
  • One-to-one: one source, one destination. A plain transfer: customer out, merchant in.
  • One-to-many: one source, several destinations. The customer pays R$103: R$100 goes to the merchant and R$3 to a fee account. Three operations, still balanced (R$103 out = R$100 + R$3 in).
  • Many-to-one: several sources, one destination. A few accounts pooling money into a single fund.
  • Many-to-many: several sources and several destinations at once, like a marketplace splitting incoming payments across sellers and fees.
The rule never changes, no matter how many parts there are: everything that leaves must equal everything that arrives.
Not every ledger supports all four shapes. Simpler systems may allow only one-to-one (or one-to-many) movements, while others handle the full many-to-many case in a single transaction. What’s possible depends on the ledger you use.
A transaction is all-or-nothing. Either every operation succeeds together, or none of them happen. The books never stay half-recorded. The name for this property is atomicity.

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Money in transit: holds and two-phase movements

Where does the money sit before a transaction is final? Many movements don’t settle the instant they start. The system first reserves the amount: it’s set aside, still in the account, but no longer free to spend. Then the transaction either commits (settles for good) or cancels (releases the reservation). This is a two-phase movement: reserve first, then commit or cancel. An account’s money has two parts:
  • Available balance: what you can actually spend right now.
  • Held balance: what’s reserved for a movement that hasn’t finished. Still yours, just frozen in place until it settles or releases.
Think of a hotel pre-authorization on your card. At check-in the hotel reserves an amount. It isn’t gone, but you can’t spend it. At check-out the charge commits, or the hold is canceled and the money frees up. Same money, two phases.

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Spending control

Once you can see money as available versus held, controlling spending becomes natural. At any moment, an account’s money sits in one of three states:
  • Available: free to spend.
  • Held: reserved for a movement in progress (in transit).
  • Blocked: frozen on purpose, set aside so it can’t move at all.
On top of that, limits can cap movement. A limit sets a ceiling on how much can flow. Together, these answer a common question: why can’t this account spend? Usually the reason is a hold, a block, or a limit, not missing money.

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Next steps

See it in LerianSee these ideas in practice: Transactions, Operations, and Balances.