Doing a bit of thinking of how to frame up some of the differences between traditional, digital and social initiatives—each has it's own set of properties, there is some overlap and there are also distinct characteristics. Thought it might help to apply them to a "spectrum of engagement"—the thought is that the more you move away from broadcast—(one way communication towers), the more participatory behavior and engagement with the business/brand etc will be had. The point isn't to replace any of these or place them in silos, but to simply illustrate a range at a high level.
This is the marketing advertising mix that's prevailed over the years and has been perfected through broadcast and mass media techniques supported by a ratings system. It also could include some traditional PR, direct etc.
Digital marketing has moved beyond it's infancy years and matured into something that's partially interactive, holds more promise for engagement, but incorporates traditional methodology. For example, a traditional Website may be interactive and technology dependent, but doesn't allow for user participation, feedback mechanisms reviews etc. Engagement can be increased through tactics such as interactive games or even a rich user experience, but there are no social components. Search methodologies are limited to things such as keyword, search optimization etc.
Social engagement is created when design for participation is the primary strategy for the associated initiatives. Tactics can range from the simple to complex, but is primarily tasked with facilitating interactions from participant to participant to organization to participant(s) and vice versa. Social engagement carries distinct characteristics compared to "tradigital" in that it requires not only technology, but human intervention on the part of the organization in order to achieve the highest levels of engagement.
The gaps in between each stop represents where lots over overlap can exist. Anyway, it's a high level model. Thoughts appreciated.