Omniscience is God's ability to know everything there is to know.
Some have questioned whether omniscience is compatibile with free will; specifically, Calvinists have argued that God knows whether a person will be saved before he is born.
However, knowing what the outcome of a man or woman's free will will be does not mean that (s)he does not have free will. It is possible for God to know how a man or woman will exercise their free will and at the same time not interfere with it.