What on earth is dragonglass?
Also known as obsidian, dragonglass is a volcanic glass that is very handy for killing white walkers. You might remember Samwell Tarly using it early on to save Gilly from a white walker — earning him the (sort-of ironic) nickname “Sam the Slayer”.
The children of the forest make their weapons out of dragonglass. Blades using obsidian are sharper than steel but far more brittle and the Valyrians used to call obsidian frozen fire. Folklore has it that dragonglass is made by dragons, but the Maesters believe it comes from the fires of the earth. Obsidian is actually a type of volcanic rock real world, but the Game of Thrones version is much more magical.
Why should I even be paying attention to all this dragon-talk?
It looks as though Game of Thrones is building up to one epic battle between ice and fire, white walkers and dragons, the Night’s King and Daenerys. If this plays out the way we’re expecting (although known George RR Martin there are still a few twists and turns waiting), Westeros are going to need a whole heap of dragonglass. So it’s a good job you now know what it is.