Fortron is a form of energy that MFFS machines use as a source of power. It is produced and stored initially by the Coercion Deriver to then be transferred to other machines by the Fortron Capacitor.
Another source of Fortron energy is a creative-only item known as the Infinite Power Card. It can be placed directly into a Fortron Capacitor (left most item slot) to provide an infinite supply of Fortron.
Fortron is able to exist as a liquid. It may be pumped directly from a Capacitor and manipulated in the same way Water or Lava can.