In certain forms of government, "reserved powers" are all powers not explicitly assigned to a specific authority. Federation or confederation forms of government that are composed of smaller, decentralized political units (like states) generally make a blanket determination as to whether reserved powers lie with the central government or with the state and local governments.
Since it is practically impossible to list every possible governmental power in a central government's framing documents, these documents generally include all unwritten powers as "reserved powers" and specify whether the federal government or the state governments are to hold these powers. Two examples of countries that operate in this manner are Canada and the United States. Canada leaves its reserved powers in the hands of the federal government, whereas in the United States they are given to the individual states.
The Tenth Amendment of the U.S. Constitution specifies that powers not otherwise delegated to the federal government or prohibited to the states fall to the states or to the people. Some issues fall into a legal grey area, however, as exemplified by the use of cannabis. Though the federal government classifies it as an illegal drug, many state governments have provisions for use of it for medical purposes, and as of 2014, recreational use has been legalized in the states of Colorado and Washington.