Salis Mundus (a.k.a. Thaumaturge's Salt) is an easily-made crafting material that is used in Alchemy and Infusion Enchantment. Essentially, it represents a dose of "pure power" for certain high-energy creations.
Salis Mundus is created by making Balanced Shards (in the Crucible or Thaumatorium), and then smelting them.
In older versions, Salis Mundus was crafted at an Arcane Workbench, using Crystal Shards and either Ethereal Essence or Mana Beans. Both recipes were shapeless, and the ingredients could be of any aspect.