Interest v Affinity

Affinity groups are typically religious or cultural in nature. Like a youth group for a church or a student association for people of a particular ethnic background. Basically, they're defined by the people in them. Interest clubs or groups are predicated around a common interest, which are usually more oriented around a particular subject, pastime, or topic—like a creative writing club, or a coding club, or a Robotics team. Hope that clarifies things.