What is Patent Infringement?

Legal Definition
Patent infringement is the commission of a prohibited act with respect to a patented invention without permission from the patent holder. Permission may typically be granted in the form of a license. The definition of patent infringement may vary by jurisdiction, but it typically includes using or selling the patented invention. In many countries, a use is required to be commercial (or to have a commercial purpose) to constitute patent infringement.

The scope of the patented invention or the extent of protection is defined in the claims of the granted patent. In other words, the terms of the claims inform the public of what is not allowed without the permission of the patent holder.

Patents are territorial, and infringement is only possible in a country where a patent is in force. For example, if a patent is granted in the United States, then anyone in the United States is prohibited from making, using, selling or importing the patented item, while people in other countries may be free to exploit the patented invention in their country. The scope of protection may vary from country to country, because the patent is examined -or in some countries not substantively examined- by the patent office in each country or region and may be subject to different patentability requirements.
-- Wikipedia
Legal Definition
Violation of a patent owner's rights with respect to some invention. Unless permitted by the patent owner, one commits patent infringement by making, using, offering to sell, or selling something that contains every element of a patented claim or its equivalent while the patent is in effect. For infringement to occur, the prohibited act must be done in the United States or a violating product must be imported into the United States after being created abroad. See 35 U.S.C. ยง 271(a).
Legal Definition
a term that is used when a person's patent is violated or encroached upon.