Dear student,
Residuary subjects are matters which are not included in any of the three lists. The Constitution of India provides for a division of powers between the centre and state governments. It divides all the subjects into 3 lists - Union List, State List and Concurrent List. The Union List describes the subjects under the control of the central government, the State List describes the subjects under the jurisdiction of state governments, and the Concurrent List describes the subjects which are under the joint jurisdiction of the central and state government.
The subjects which do not fall in these lists are called as residuary subjects. The right to make laws on these subjects is called residuary power. The right to legislate on these residuary subjects rests solely with the central government.
Thank you.