debit
/ DEB-it /
Imagine every account in a business as a box with two sides, a left side and a right side. A debit is simply an entry written on the LEFT side of one of those boxes. That is the whole literal meaning — left side. It is one of the two directions in which money information can flow, the partner of its opposite, the credit, which goes on the right.
The word does not mean 'increase' and it does not mean 'decrease', even though most people first guess it means one of those. Whether a debit makes an account go up or down depends entirely on what kind of account it is. For assets and expenses, a debit increases the balance: if a shop buys 500 dollars of supplies for cash, it debits Supplies for 500 (the supplies asset grows). But for liabilities, equity, and revenue, a debit decreases the balance. So a debit only ever means 'put this amount on the left side of this account'; the up-or-down effect comes from the account type.
Debit comes from the Latin debere, 'to owe', and is abbreviated Dr (from the older 'debtor'). In everyday speech a bank says it 'debits' your account when money leaves, which confusingly is the bank's view, not yours — to the bank your deposit is a liability it owes you, so a debit reduces that liability. Inside double-entry bookkeeping, though, the rule is mechanical and consistent: a debit is the left side, full stop, and accountants learn the per-element effect by heart.
A bakery pays 300 dollars cash to buy flour. It records a debit to Inventory of 300 (an asset goes up, recorded on the left) and a credit to Cash of 300 (another asset goes down, recorded on the right).
The same 300 sits on the left of one account and the right of another, so debits equal credits.
A debit does not mean 'subtract' or 'bad'. It only marks the left side; whether the account rises or falls depends on the account's type and its normal balance.