Is a Program Manager a person who manages mutiple projects (under a single program) which are in turn managed by Project Managers?
Or is a Program Manager a person as defined by Joel Spolsky here.
NOTE: I am not referring to this.
I suppose the answer hinges on what the terms "Program" and "Project" mean.
According to Project Management Institute (PMI), The Standard for Program Management, 2nd Ed., "A Program is a group of related projects managed in a coordinated way to obtain benefits and control NOT available from managing them individually. Programs may include elements of related work outside of the scope of the discreet projects in the program... Some projects within a program can deliver useful incremental benefits to the organization before the program itself has completed."
To add to @Robert's answer...
Different companies may use titles in different ways, so if you're asking because you want to know what a title means at a certain company, you may want to inquire on a case-by-case basis as not everyone will use the same reasoning.
The way I've seen it done ( may be fairly common in aerospace.. might be just my experience)
Program manager manages the program
A program has projects. (Often for specific customers)
So the program manager has to take a longer term view, guide things to be more strategic. "We're going to need that later". "Can't cut that corner". "Have to ship today, project must dovetail with other project that hasn't been announced to rest of company yet"
The project manager worries about THIS project.
I've seen the Program manager as basically the Project manager's boss.
It REALLY helps if they don't fight.
It really appears to depend on the company.
At Sun, they had program managers who were essentially interfaces between the technical teams and the bureaucracy. One program manager would be assigned to several such teams and would make sure that, say, the required information is passed to the various architecture boards, open-source licensing policies are maintained, and they would convene regular status meetings of "program teams" that included the technical teams plus associated marketing and other folks.
This usage is perhaps vaguely related to some of the other explanations given here, but you can see that it really depends.
Michael Lopp wrote an article recently with a comparison I quite liked.
First, some definition. Project manager, product manager, and program manager. Let’s clear that up. A project manager is responsible for shipping a product, whereas a product manager is responsible for making sure the right product is shipped. A program manager is an uber-mutated combination of both that usually shows up to handle multiple interrelated projects like, say, an operating system. Different companies use the names differently, but for this article, project = ship the product, product = ship the right product, and program = ship many interrelated products, usually at the same time. Got it?