The Father, the Son, and the Holy Spirit. These three do not exist independently of each one another, but rather exist in relation to one other. For example love is a relation, and each of the persons love one another. The Father loves the Son. The Son loves the Father.
Love is the relation in the relationship.
Here is where things get weird. Not only are the 3 persons of the Trinity, related to one another through one means or another. They are the relations themselves. Indeed God is love itself, not just the loved one. In fact God is lover, the loved one and love itself.