Deferred tax is basically the impact that a difference between the tax treatment and the accounting treatment of a transaction has.
For example, let’s say that a company has losses for the past 3 years and it believes that it will do better in the future (that it will make a profit) so the tax losses will be used against future taxable profits.
In this case, the tax treatment of these losses show an asset (something like a prepaid expense if you want to think about it like that). However, there is no such thing for accounting purposes. Therefore, a deferred tax asset arises to reflect the fact that for accounting purposes we have understated our assets and we will be able to utilize a tax asset in the future.
Similarly, depreciation can be treated differently for accounting and tax purposes. For this reason, if you have underclaimed depreciation for tax purposes, you should have a deferred tax asset but if you have overclaimed depreciation expense, you will have a tax liability.