What is the difference between a Program Manager and Product Manager? Is there actually a difference in the roles/responsibilities or our the terms mostly used interchangeably.
Depends entirely on the company. Microsoft, for instance, has its own rather unusual definitions:
Program Manager = one of the members of the core technical staff (alongside developers and testers). Typically responsible for designing & specifying features, planning release cycles, triaging bugs, presenting at technical conferences, managing compliance with technical regulations (internal & governmental), connecting with online communities, and more.
Product Manager = basically a synonym for "marketing suit." They design the product's ad campaigns, sales website, and related swag. More generally, they define the "message" that they hope people (mainstream media, word-of-mouth, and everything in between) will associate with each release.
Both positions gather a lot of data about where the market is heading -- Program Managers from their relationship with the technical community, Product Managers from their industry & media contacts -- but the ultimate decisions about what to build are made by someone higher in the chain. (not the nitty gritty, of course; Program Managers & UX designers are the experts at specifying the details. thinking more of "vision" / "value props" that individual product subunits then go "align" themselves toward)