Predestination, in Christian theology, is God’s decision that specific things will happen. Augustine of Hippo and John Calvin (among others) suggested that God purposefully chooses who will be saved and who will not. This controversial idea has some basis in Scripture, but is undermined by many passages throughout the Bible.
Calvinism is a system of Christian thought known for a specific view of the predestination of believers. Molinism is a lesser-known system with a different view. If you've ever wondered about soteriology - that is, the doctrine of salvation - this podcast might be helpful to you.