The short answer would be the first answer to this question: "A program is a group of projects".
However, the long answer has to examine the different from several angles:
- Vision: the project is restricted in its vision to the requirements, the program has the whole business strategy of the company in its vision.
- Length: the project is limited in length, the program, on the other hand, is either unlimited or has a much longer length than a normal project.
- Management: Management of a project is done by a Project Manager, management of a program is done by a program manager.
There are also other differences concerning resources and risks.