Depreciation is the assigning or allocating of a plant asset's cost to expense over the accounting periods that the asset is likely to be used. For example, if a business purchases a delivery truck with a cost of $100,000 and it is expected to be used for 5 years, the business might have depreciation expense of $20,000 in each of the five years. (The amounts can vary depending on the method and assumptions.)
In our example, each year there will be an adjusting entry with a debit to Depreciation Expense for $20,000 and a credit to Accumulated Depreciation for $20,000. Since the adjusting entries do not involve cash, depreciation expense is referred to as a noncash expense.