A more thorough explanation:

The first-sale doctrine is a legal principle that applies to both copyright and patent law. It allows the purchaser of a physical copy of a copyrighted work or a patented article to sell or give away that copy without infringing on the owner's exclusive distribution rights.

Under copyright law, the first-sale doctrine means that if you buy a book or a CD, you can sell or give away that copy to someone else without breaking the law. The copyright owner's distribution right is said to be exhausted with regard to that physical copy.

For example, if you buy a copy of a book and then sell it to a friend, you are not infringing on the author's copyright. The author cannot control what happens to that physical copy of the book once it has been sold.

Under patent law, the first-sale doctrine means that if you buy a patented article, you have the right to use, repair, and resell that article without interference from the patent owner. The patent owner's monopoly right to control the use of the article is said to be exhausted with the first sale.

For example, if you buy a patented tool and then sell it to someone else, you are not infringing on the patent owner's rights. The patent owner cannot control what happens to that physical tool once it has been sold.

However, the patent owner may still be able to retain some control over the article through terms in the license or sale contract. As long as these limitations do not amount to anticompetitive patent misuse, they are allowed under the law.