Corporate Strategy talks about what market a firm decides to pursue. All firms must make the basic decision as to how many businesses it will enter and the priortization of these businesses (i.e., how will it divide its resources).
A good primer on the basics of corporate strategy.
Article by one of the chief scholars in the field, Richard Rumelt.
The growth-share matrix (aka the product portfolio, BCG-matrix, Boston matrix, Boston Consulting Group analysis, portfolio diagram) is a ...
Professor Richard Rumelt says its simply the focus of resources on business objectives.