An entity with legal rights and existence including the ability to sue and be sued, to enter into contracts, to receive gifts, to appear in court either by themselves or by lawyer and, generally, other powers incidental to the full expression of an independent entity in law.
Individuals are "persons" in law unless they are minors or under some kind of other incapacity such as a court finding of mental incapacity.
Many laws give certain powers to "persons" which, in almost all instances, includes business organizations that have been formally registered such as partnerships, corporations or associations.
For example, the US Code defines "person" as follows (at Title 1, Chapter 1, ¶1):
"The words person ... include(s) corporations, companies, associations, firms, partnerships, societies, and joint stock companies, as well as individuals."