A portfolio is comprised of multiple programs or multiple projects. For example, I oversee a medical device portfolio at MSK. There are multiple related and non-related devices that make up the portfolio. Our strategy is to market the devices as a portfolio for industry to license. The portfolio can be broken down into segments/programs for example, gynecological devices or research tools etc. As ec52 and aaq2 mentions, grouping of programs into strategic portfolios known as portfolio management is useful to implement business objectives.