Costs that are matched with revenues on the income statement. For example, Cost of Goods Sold is an expense caused by Sales. Insurance Expense, Wages Expense, Advertising Expense, Interest Expense are expenses matched with the period of time in the heading of the income statement. Under the accrual basis of accounting, the matching is NOT based on the date that the expenses are paid.
Expenses associated with the main activity of the business are referred to as operating expenses. Expenses associated with a peripheral activity are non-operating or other expenses. For example, a retailer's interest expense is a non-operating expense. A bank's interest expense is an operating expense.
Generally, expenses are debited to a specific expense account and the normal balance of an expense account is a debit balance. When an expense account is debited, the account credited might be Cash (if cash was paid at the time of the expense), Accounts Payable (if cash will be paid after the expense is recorded), or Prepaid Expense (if cash was paid before the expense was recorded.)