Which of the following best defines a business expense?

The definition of a business expense is best captured by the option stating that it includes costs incurred in the ordinary course of business that can be deducted from income. This highlights two essential elements: the operational context and the tax implications.

When defining a business expense, it is important to note that expenses must be ordinary and necessary for the business's operation, meaning they are typical and appropriate for the business's nature and industry. Furthermore, these costs have a significant tax aspect; they are deductible from the income, which reduces taxable profit and thus lowers the tax liability of the business.

By contrast, personal costs incurred by a business owner do not qualify as business expenses because they are not directly related to the operations or income-generating activities of the business. Marketing expenses alone do not encompass the full range of business expenses, as they represent only one category rather than the general principle of deductibility from income. Lastly, not every cost that aims for profit is a business expense; expenses must specifically be linked to the operations of the business and conform to tax regulations to qualify for deduction.