Hello jot!
“JOAT” is short for “Jack of All Trades.” Your villager can become a “JOAT” when he/she has mastered all 6 skills: Farming, Building, Research, Healing, Parenting, and Devotion.
There are 2 trophies in VV5 which require villagers who have mastered all 6 skills: “Jack of All Trades” and “Plentiful Polymaths.”