Xbox.com: Here's a silly question: Why is it called Radiant A.I.? What does that mean?

Gavin Carter: The "Radiant" part of the title refers to the way a character's awareness isn't strictly limited to a few hard-scripted objects or activities. It radiates out into the surrounding environment and beyond. They can choose to interact with anything they come into contact with based on parameters we set up when we create them.

This includes having conversations with one another, sitting down and reading books, buying food and supplies from shops, farming, exploring, engaging in combat with creatures or one another, and a wide range of other activities.