The Catechism in Questions & Answers

67. What does the term “Father” mean when it is used in relationship to God?

When the term “Father” is used in relationship to God, it is associated with divine aspects of creatorship, authority, and loving care. God is the source and sustainer of that which He has created. In this respect, all human beings are able to address God, who is their Creator, as “Father”.

See also Child of God: explanation of Question 530.