Taming is an action that can be used to Turn a feral Unit to your side, even if you cannot normally produce that Unit type.
The Arkenhammer has the power to Tame wild Dwagons and is often used by Stanley for that purpose.
A Unit can also be tamed without Magic Item or Artifacts, as Jillian did in IPSF45 for the Yellow Dwagon she later named Crapsack through giving the feral Dwagon several High Elves to eat.
"Taming" may be some form of Natural Turnamancy that any Unit may attempt, and can be given various modifiers including using Food and Magic.
Real World References
Tame appears to be similar to the real world action of taming or domesticating wild animals.