From Feral run at the Creatures Wiki:
A feral run is where you hatch a group of norns, teach them words and a few other things (like food and herbs being good and weeds being bad), inject any COBs or Agents into Albia or the Ark, and leave them to grow up for a while, interfering when you like.
Please check the Creatures Wiki before posting new topics asking for definitions in the future.