Accelerated Mobile Pages
Yes, its new, yes a little confusing, but preparing for the future NOW is what will benefit your website in years to come. Google have been pushing this new concept called Accelerated Mobile Pages, also shortened to AMP and is aimed to be one of the top search engine ranking indicators!
Keeping it short and sweet
Both have subtle features that add the /amp slug to all your web content pages. With the Yoast plugin you can tailor the look of the pages a little further adding colours to headings and backgrounds etc.
Give it a week and test your site in the Google Search Console AMP section.