Fixed costs can be defined as:

Fixed costs are best defined as costs incurred regardless of production volume. These costs remain constant over a specific range of production or sales levels, meaning that they do not change as the volume of output increases or decreases. Common examples of fixed costs include rent, salaries of permanent staff, and insurance expenses. These expenses need to be paid whether a company produces one unit or thousands of units, which is why they are classified as fixed.

The other concepts presented in the choices refer to different types of costs. Expenses that vary with production levels are described as variable costs. Costs that only occur during peak seasons are seasonal costs, and they are not relevant to fixed costs since fixed costs remain the same regardless of production volume or time of year. Likewise, costs associated with selling products can include both fixed and variable components, particularly sales commissions, which may vary with the level of sales made. However, these do not strictly pertain to the definition of fixed costs.