In such context, a bottleneck link for a given data flow is a link that is fully utilized (is saturated) and of all the flows sharing this link, the given data flow achieves maximum data rate network-wide.
In such a scenario, a saturation point link for a specific data stream is a connection that is completely utilized (is congested) and among all the flows sharing this link, the given data stream achieves the maximum data rate network-wide.