To resolve the asymmetry of the directed k nearest neighbours relation, we drop edge direction: nodes $i$ and $j$ are connected by an undirected edge whenever $i$ is among $j$'s k nearest neighbours OR $j$ is among $i$'s k nearest neighbours. This 'OR' rule is what is usually meant by the k nearest neighbours graph, and it is looser than the mutual k nearest neighbours graph, which requires the relation to hold in both directions.