A program is a group of projects.
Their management is coordinated because they may use the same resources, the results of one project feed into another. A definition of a program is An undertaking where there is a vision of an outcome – BUT no clearly defined path of getting there. Program management is the co-ordinated management of related projects, which may include related business-as-usual activities that together achieve a beneficial change usually of a strategic nature for an organization.
Portfolio management is the selection and management of all of an organization’s projects, programs and related business-as-usual activities taking into account resource constraints. Describes the investment business has in itself. Portfolios are about maximizing return on investment.