Expenses can be grouped into different categories based on their nature, function, or relation to the revenue. Common expense categories include cost of goods sold (COGS), which are the direct costs of producing or purchasing the goods or services that are sold to customers, and operating expenses, which are the indirect costs of running the business, such as rent, utilities, salaries, marketing, depreciation. Non-operating expenses are also important to consider and refer to costs that are not related to the core operations of the business, such as interest, taxes, losses from discontinued operations, or extraordinary items. It's essential to identify which category your expense belongs to since it affects how you report it in the income statement and measure its impact on the profitability of the business.