A cheesy substance used in the manufacture of projectiles, thrusters, and pistons. Weighs over two tons per gram.
Now, maybe you're familiar with the popular british sci-fi comedy series, Red Dwarf, and maybe you're not, but this really is not such a good name for a product, considering the actual definition of the word smegma. One can only hope there is little or no connection.
The joke about the substance's weight indicates that it's more than 2 million times as heavy as itself, which is... pretty much impossible. Yeap.