Change address
Change output
A change address is a new address of your own wallet that receives the leftover amount when a transaction spends more bitcoin than the payment needs.
Bitcoin is spent in whole coins (outputs). Paying less than a coin’s full value sends the payment to the recipient and the rest, minus the fee, back to a change address the wallet derives, usually on a separate internal branch of its key tree under BIP32.
Change is still your money. A signing device that understands PSBTs can recognise change going back to its own wallet and show only the real payment for confirmation.
Change outputs link transactions together, which is one way observers group addresses. See does reusing a bitcoin address hurt my privacy?
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