What is meant by the attributes of God?

The attributes of God are those unique qualities and perfections that inhere in and manifest the being or essence of God.

By saying the attributes inhere in the divine essence is meant that they are more than a list of adjectives or characteristics that describe God; they are the essential conflation of divine qualities without which he would cease to be God. God is what his attributes are.

By saying that the attributes manifest the divine essence is meant that God is known only through his attributes.