The direction of a relationship shows if the relationship can be interpreted in one or both directions.
There is only two options:
A directed relationship models asymmetric relations (ie the relationship can be interpreted in only one direction)
It represents a Relationship between a collection of source model elements and a collection of target model elements. A Directed Relationship is said to be directed from the source elements to the target elements.
An Undirected relationship models a symmetric relations (ie the relationship can be interpreted in both directions)