The term portfolio is use to refer to a collection of programs and projects.  These programs and projects are initiated, prioritized, and managed by a company to meet the goals of the business.   The term program is use to refer to a single strategic business initiative and groups one or more related projects that support the business initiative.  So one or many related projects can make up a program and one or many programs can comprise a portfolio.

As a business analyst, understanding each of these three concepts (portfolio, program, and project) and how your project fits into the greater program and ultimately portfolio of projects can help you understand many of the decision made by executives.  If you know that your project has a high priority within the portfolio, your requests for additional resources have a much higher likelihood of being approved compared to a request from a low priority project.  Similarly, if your project has a low priority, resources could be pulled to support higher priority projects or your project may be cancelled altogether, even if it was on track and on budget.

Understanding other projects in the portfolio and their relation to your own can also help the business analyst make better decisions.  Instead of making decisions based strictly on a myopic view of your own project, a good business analyst will consider the pros and cons that each decision may have on other projects belonging to the same program.  In this way, the business analyst is ensuring that they are delivering the optimum solution for the project and the company as a whole.