Heartiness is a quality of being enthusiastic and warm. If you are known for your heartiness, you might introduce yourself with a vigorous and friendly handshake. Food that has heartiness is filling and good for you.
When you use the noun heartiness to talk about people, it describes their cheer, warmth, and strength. Think of the heartiness of the group at your wonderful family reunion, for example. And when it comes to food, heartiness describes something nourishing and robust, like the heartiness of satisfying dishes like stew or rice and beans.