Corporations are "artificial persons, who may maintain a perpetual succession, and enjoy a kind of legal immortality....", “are such as are created and devised by human laws for the purposes of society and government.” 
In general, a corporation is a legal entity with separate existence from those making it up. It may be constituted by one person ("corporation sole") or by a group of people ("corporation aggregate"). Today, most corporations have perpetual succession irrespective of a person or persons ceasing involvement (including by death) though corporations may have a limited life specified in their instrument of creation. By way of contrast, an unincorporated club or a simple partnership, for example, have no separate legal existence apart from that of their members or partners.
Corporations may exist in common law or under a State's constitution or be established by Charter issued under Royal prerogative or by decree or equivalent, under a statute for the purpose or by registration under powers given by statute.
In some jurisdictions some corporations sole are seen as corporations aggregate, looking at successive holders of the office over time as a group. In common law monarchies, the Crown is normally treated as a corporation sole. A single person may hold several offices as corporation sole. For example, the reigning monarch of the United Kingdom both constitutes the Crown in Great Britain and Northern Ireland and, as a separate corporation, also constitutes HM The King - or Queen - in Right of New South Wales.
Frequently, but not always, corporations are established for the purposes of undertaking particular activities. Examples of activities would be conduct of a State, municipality (e.g. Mayor of London, England) or other local or regional government activities, ecclesiastical activities (e.g. (Roman Catholic) Archbishop of Baltimore, USA) or a business (e.g. The Hershey Company, a US corporation that makes and sells chocolate and other foods).
In UK and most Commonwealth English, a corporation formed for the purposes of carrying a business is commonly known as a "company". In US English "corporation" is usually used for this meaning and "company" can take the wider meaning. US firms may, however, refer to themselves using the word "company". An example of this is the Wm. Wrigley Jr. Company, the chewing gum manufacturer merged into Mars Incorporated (another US food manufacturer) in 2008.
For more discussion of business corporations (companies) see Company.
- William Blackstone, Commentaries, Vol. 1, Chapter XVIII and Chapter 1, 1755/56, available for example at http://oll.libertyfund.org/title/2140