A non-cash expense is an expense recognized on the income statement that does not involve an actual outflow of cash during the period it is recorded. The cash outflow for such an expense typically occurred in a prior period when an asset was acquired. Depreciation is the correct answer because it represents the systematic allocation of the cost of a tangible asset, such as machinery or buildings, over its estimated useful life. While depreciation reduces a company's reported profit and the asset's book value, no cash changes hands when this expense is recorded each period; the actual cash expenditure occurred when the asset was initially purchased.
Conversely, the other options are all cash expenses. Rent expense involves periodic cash payments to a landlord for the use of property. Salary expense represents cash payments made to employees for their services. Similarly, Interest expense typically involves cash payments to lenders for the use of borrowed funds. These expenses directly impact a company's cash balance in the period they are incurred, making them distinct from non-cash expenses like depreciation.