Practitioners, analysts, proponents and critics of this thing we do with learning and technology solutions will frequently use all of these terms interchangeably to describe the discipline of using technology for connecting learners with learners, teachers, content, experts and experience. There's nothing really wrong with that. These days everybody kinda gets that "anytime, anywhere learning" uses technology to extend the boundaries of classrooms in some novel and compelling ways, no matter what we call it.
While I agree that the boundaries of these constructs are fairly fluid, they do each possess characteristics that make each unique. eLearning tends to be used when referring to Flash-based content and web-delivered, self-paced, independently completed courses built on linked modules and assessments. Collaboration and web conferencing also fit here. Distance learning has tended to depend on telephony (e.g. audiographics, compressed video) cable and broadcasting systems, using a class-room model (e.g. cohorts, start and stop on fixed schedule) for delivering distributed courses. Online learning refers to course delivered via the Internet; sometimes with a teacher, sometimes not. Sometimes with "live"/real-time web conferencing, sometimes not. Sometimes with course sylabi and digital content, sometimes not. Managed in an LMS. What is held in common is that it is an internet-dependent experience.
The reason I wanted to mention this today is that even as some of us in the education sector are getting all wound up to do battle over online learning eQuality (please refer to my past two blog posts) there are some sectors that have already moved on. They are already talking about mLearning as the new elearning. And game based learning and augmented reality as the next big thing that will replace online learning. And virtual learning getting ready to give game based learning a run for its money. (I would make a catty remark about Second Life, but I heard a rumor on the street that Microsoft may be interested in buying them so I expect it is smarter to keep quiet.) 3D learning. Rich Internet Applications for learning. And the hottest of all: Social media. Social media. Social media.
As Jean-Baptiste Alphonse Kerr once said..."plus ça change, plus c'est la même chose". We need to care about the technology, and we DO need to understand the subtleties between and among the variations of technology-based teaching we are likely to encounter. But we also need to understand the commonalities as much as the differences, and look for ways to learn from each set of evolving practices on the way. Because there will always be a next new thing. And we all have too much to do to keep starting over every time we get distracted by something new and different.