Pulse and glide works like this: let's say you're on a road where you want to go 60 km/h. Instead of driving along at a steady 60, you instead accelerate to 70 (that's the pulse), and then coast in neutral with the engine off down to 50 (that's the glide). That's it. Rinse and repeat. And repeat. And repeat...
By doing this, you're still averaging 60 km/h, but it turns out that pulse and glide is significantly more efficient than driving along maintaining a steady 60 km/h.
via metrompg.com