What is predestination?

Predestination is a religious concept that is most closely associated with the Calvinists in the aftermath of the Protestant Reformation.
In the early 16th century, Martin Luther campaigned against the Catholic Church by exposing corrupt practices.  This culminated with his famous 95 theses, nailed to the door of a Catholic Church in Wittenberg, Germany. As a result of the religious upheaval in Northern Europe, many different branches of Christianity fractured from Catholicism. One of those followed John Calvin and his ideas on predestination.
Predestination is the idea that God decides whether a person is destined for heaven or hell. This is contrary to other groups at the time, like Protestants (who believe that through faith alone one can get into heaven) or Catholics (who believe faith and good works can get a person into heaven). Calvinists believe that their place after death has been decided—faith or good works could not change your course. Being a "good Christian" could, however, affect your time on earth and the community in which you lived, so despite believing that they could not change their final destination, Calvinists still obeyed the Commandments and Biblical teachings.