What's a better (i.e., non-PowerPoint) term for 'slide'?

Personally, I would promote the content, rather than the media. It isn't the term slide that locks our thinking in the last century, it is the concept. We need to start thinking in terms of what it looks like to the learner. They should be presented with content; objects that appear, move, interact, and disappear. They should have the opportunity to interact, stop, or move on through the content, as they (and it) dictate. In reality, the learner doesn't know, doesn't need to know, and doesn't benefit from knowing whether they are seeing 100 slides, each with one object on it, or one slide with 100 objects on it.

Again, this is my opinion, but the ideas of "Next" and "Previous" cause a lot of damage here. Since the invention of hypertext, learners should not be thinking in terms of pages and slides. It is worth the extra effort of creating your own clickable objects (personal bias: buttons in SL come with too much baggage. I use objects, or filled text boxes) that allow the learner to "Continue",  "Review", or "Select what to do next".  This can be done even by those of us who work for the government, (or other clients) that force us to create projects that contain thousands of slides, each with 400 words on it that are navigated in a linear fashion.