Vocabulary - Cut

A cut is a partition of nodes into two sets $S$ and $T$, where the source is in $S$ and the sink is in $T$. The capacity of the cut is the sum of capacities of edges from $S$ to $T$. The minimum cut has the smallest capacity.

By the max-flow min-cut theorem, its capacity equals the maximum flow. Finding the min-cut reveals the bottleneck edges in the network. These edges limit the maximum throughput.