Friendly vs. Responsive

Mobile-friendly sites aren’t necessarily designed specifically for a mobile device. Rather, they’re versions of sites that work across different devices. Think of a mobile-friendly site as mobile-optimized, whereas a responsive site is mobile-first. A site that’s mobile responsive changes – or responds – based on the device it’s viewed on. 

Responsive vs. adaptive

Responsive sites adjust to any layout. Adaptive sites, on the other hand, only adapt at select points.