Double-entry accounting
Also known as: double-entry bookkeeping
Double-entry accounting records every transaction in at least two accounts, with total debits always equal to total credits.
In a double-entry system, money never simply appears or disappears: it moves. Each transaction has a source and a destination, recorded as balancing debit and credit entries. Paying a $500 bill, for example, credits (decreases) cash and debits (increases) an expense by the same $500.
Because debits and credits must always balance, the system is self-checking: if the books don't balance, something was recorded incompletely. This is the foundation every financial report is built on.