What is deferred revenue expenditure?

here is an example that should help you more than the dry language of it:

Accounting value

$1,000

$800

$600

$400

$200Tax value$1,000$750$563$422$316Taxable/(deductible) temporary difference$0$50$37$(22)$(116)Deferred tax liability/(asset) at 35%$0$18$13$(8)$(41)