A corporation is established in terms of a Companies Act or the like in terms of Corporate Law (particulars depend on the jurisdiction).<p>A corporation is a legal person, but not a natural person. 
A corporation is not an agreement between a group of people. People can agree to <i>form</i> a corporation, but the corporation itself is not an agreement (merely the end result). For example, a corporation can act <i>against</i> the interests of the people who founded it.