I think of it in terms of when it is expensed vs when it is deductible. If an expense occurs in the current year but is not deductible until the proceeding year it potentially creates a Deferred Tax Asset so long as it becomes deductible in the future. A deferred tax liability stems from a deduction taken in the current year but is not expensed until the next year.
For instance: Warranty expense is booked at the time of a sale based on management's estimate; however, the only portion that is deductible is that of which has been performed and paid. This creates deferred tax assets the company will take in the future as they perform the warranty services.
The difference between straight line depreciation management used for assets and MACRS of the IRS can create an expense that is deductible in the current year that will not be booked by the company until a future period. This creates a deferred tax liability that will eventually become payable in the future.
Disclaimer: This may not be a textbook definition and it is only the way my mind comprehends the concept.
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