It's tempered auto (or other) glass that breaks into 'crumbs' rather than into large, dangerous shards. In cars it is usually found in the side windows. While it can withstand pretty heavy blows from blunt objects, even a relatively light peck from something hard and sharp pointed can shatter it. A lot of rescue tools take advantage of this fact in various ways- see examples at
A good bit of large glass surfaces you see are tempered glass as well- I had a sliding glass door in my home shattered from being struck with a rock thrown by a lawn mower.