Copyright and patent power is a power given to Congress in Article 1, Section 8, Clause 8, in the U.S. Constitution. This power enables Congress to grant exclusive rights for a period of time to inventors and authors for their work. According to the Constitution, Congress was given this power in order to "promote the progress of science and useful arts."
Copyright and patent power is basically just the right that Congress has to issue copyrights and patents. If citizens know that the rights to their intellectual property and inventions will be protected by the government, then they have more incentive to create such inventions and intellectual property. If anyone could just steal their ideas as soon as they came out with them, then people may be less inclined to create original work. This is why Congress was given copyright and patent power in the Constitution.