Corporation

an institution that is granted a charter recognizing it as a separate legal entity having its own privileges, and liabilities distinct from those of its members.[1] There are many different forms of corporations, most of which are used to conduct business. http://en.wikipedia.org/wiki/Corporation

see: Business Structure (for subtypes), BigCo, SmallCo, Start Up

In theory its value is driven by the time-discounted likely-future stream of Profit. But see Security Analysis.