What do you mean by residuary powers?

Indian Constitution mentions the legislative powers which are divided between Union and the state government in a threefold way. These three lists are – Union list – it includes the subjects of national importance such as defence of the country, foreign affairs, banking, communications, and currency; State list – it includes the subjects of state or local importance such as police, trade, commerce, agriculture and irrigation; concurrent list – it includes the subjects of common interest to both union and the state government such as education, forest, trade unions, marriage, adoption, and succession.

The subjects which are not included in these three lists are considered as residuary subjects such as computer software. The decisions related to such subjects are taken by the Union government as mentioned in the Constitution. This is referred to as Residuary powers.