De minimis is a legal term implying that a matter is trivial and it is not appropriate to pursue it.
Most commonly, de minimis refers to very small financial amounts or differences.
De minimis amounts for tax purposes are ones which are disregarded for particular rules.
For example, the UK's Corporate Interest Restriction rules have a de minimis amount of £2 million for a worldwide group.
This means that groups will normally be able to claim tax relief on at least this minimum amount of interest expense.