Copha is solidified coconut oil that will stay solid at room temperature. It comes in blocks or a cube wrapped like butter or dripping. It is white, but goes clear when melted.
It is basically coconut butter that has been hydrogenated to make it even more stable until deliberately melted, and to make it more resistant to going rancid (it's treated with a hydrogen gas that changes unsaturated fat bonds to saturated ones.)
Copha is the brand name in Australia. Kremelta is the New Zealand version, and Palmin is the German version, both of which are the same as Copha except for the brand name.
If you are outside of Australia and desperately looking for a substitute to make "Chocolate Crackles" (balls made of melted chocolate and Rice Bubbles, or what the rest of the world calls Rice Krispies), see the recipe section for a healthier version of Crackles that doesn't use Copha. Now, granted, when you're eating something like Chocolate Crackles, "healthy" isn't the point, so let's say instead a version that doesn't use Copha for when you can't get it.