Under United States law, a patent is a right granted to the inventor of a (1) process, machine, article of manufacture, or composition of matter, (2) that is new, useful, and non-obvious. A patent is the right to exclude others from using a new technology. Specifically, it is the right to exclude others from making, using, selling, offering for sale, importing, inducing others to infringe, and/or offering a product specially adapted for practice of the patent.
Patent law is designed to encourage inventors to disclose their new technology to the world by offering the incentive of a limited-time monopoly on the technology. This limited-time term of patent is 20 years from the earliest patent application filing date (but this term can be extended via patent term adjustment). After the patent term expires, the new technology enters the public domain and is free for anyone to use.