From adaptive approach...
Back in past adaptive design was a nickname of principle of creating tailored mobile experience alongside the desktop website. This is how we ended up with these horrible m. (mobile) websites, which due to overhead of two websites maintenance (mobile and desktop) always failed on promise of delivering proper mobile service, raising users' frustration all the time. Simply, the editors were unable to provide the same content and features as on desktop version because this task involved a lot of manual content and media adjustments to fit requirements of different layout. Personally I gave up with dozen of websites forcing me to use their crippled mobile versions (I'm looking at you Huffington Post!) and not allowing bring back the standard desktop frontend.
...to responsive approach
Thanks to adoption of CSS3, designers were able to employ a different approach, called responsive design, which was basically a set of rules for web browsers to modify displayed website layout depending on the size of their viewport (visible screen size). It resolved the problem of adaptive design approach, as organizations had finally only one website to maintain, which have been adjusting its display to the visitor's device. This was truly revolutionary as finally we were able to delivery exceptional mobile visitor's experience at the same pace as desktop version and take care of highly growing mobile traffic in a proper manner.
Unfortunately, with increasing number of different mobile devices, responsive design approach get us into a trouble again. First, to support different devices like smartwatches, cell phones, smart phones, phablets, tablets, desktops and retina laptops and desktops (phew!) we had to start delivering frontend able to serve all of them and even taking care of subtle differences in their capabilities, what naturally drove development complexity and raised project's costs. What even worse, since it was a browser to adjust a website layout dynamically on the moment of its display, we had to transfer all of the frontend code and media for all supported devices first, what exponentially increased data transfers to visitors. Normally it isn’t a big issue, as our cellular networks are constantly increasing available bandwidths, however mobile users still stay very sensitive for data transfers due to transfer caps imposed by operators and natural changes of bandwidth available to them due to connection conditions. Obviously, the fact that even a poor smartwatch has to process a frontend code of all its bigger brothers and sisters prior displaying a simple website doesn't help with performance and consequently a proper user experience as well.
In the end of the day, only those of us who are lucky enough to be connected on rock-solid LTE, with a robust flagship phone felt a real improvement in a mobile experience delivered by responsive design.
Back to adaptive again! (or RESS)
In this situation, we had to start building smarter solutions, which will limit development complexity, but also amount of data transferred to users, offloading heavy processing on new shiny servers we buy to support our online environments. This is how we came up with new approach, vaguely called adaptive desing again (some of us call it server side responsive, or more often RESS - Responsible Design with Server Side components).
This time, instead of building specialized mobile websites, we started building smart CMS solutions, able to display same content but in different layout dynamically, selecting best experience for a visitor's device. What's more, thanks to integration with external mobile devices' databases, we could start not only recognizing the type of device (mobile, tablet etc.), but also its capabilities (touch capable, onboard GPS etc.) and subsequently customize user's experience even more.
Imagine, entering a website, which already knows that you're accessing it on a new iPhone 6s+, hence omitting navigation sliders (to let you interact with it by touch) and displaying a contact map with your position marked on it, due to native connectivity with built in GPS device. In the same time, if you visit it on your old Blackberry, it will gladly expose all navigation elements and even display resolution optimized images, saving your time and bandwidth.
What's there for web marketer?
Modern adaptive design capabilities of CMS systems simplified development and further enhancements of the websites (your development team delivers separate pieces of layout without all the dependencies) and increased our capabilities to build and deliver truly mobile optimized and personalized websites. In order to make it happen, your CMS system has to be smart enough to enable developers employ adaptive design approach easily, then deliver well performing websites at scale. This is where the battlefield is today as only a handful of solutions available on the market are mature enough to satisfy all the requirements. Whenever you select a technology or its provider, ask for their support of dynamic adaptive design, mobile experience optimization and understanding of challenges of present. No organization can afford today, to deliver inferior mobile user experience, since this is how majority of web traffic is generated in modern Internet and will be only growing in next years.