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 a situation where a particular data transmission is taking place, a chokepoint connection is one that is fully utilized (is congested) and, out of all the links involved in this data stream, it determines the overall data transfer rate across the entire network.