Back in September, Google introduced new markup for paginated content in an effort to return single-page versions of content in search results, when the content is broken up among multiple page. This would include things like multiple-page articles and slideshows.
The markup is rel="next" and rel="prev".
Google says users usually prefer the single page format, and as a consumer of content, you probably agree in most cases. But tt's worth noting that the markup isn't an absolute must. Even Google acknowledges that there are times when paginated content makes sense. Sometimes single-page versions can load slowly, for example.
Google Developer Programs Tech Lead Maile Ohye says, "Remember that if you have paginated content, it’s fine to leave it as-is and not add rel=”next” and rel=”prev” markup at all."
She created a video going more in depth on using the markup.
She has actually put together a 37-page slideshow on the subject as well:
Keep in mind, if you're in e-commerce, this all applies to you too. It's not just about writing articles and creating slidehsows. It could very well include product categories that span multiple pages.
Google does say that using the markup provides "a strong hint" that pages should be treated as a "logical sequence".
By the way, notice that in the video, we have another Googler using a Mac.