In the context of HPC interconnect networks (Infiniband, OmniPath, ...), I've come across the notion of the N½ value of the network, which is supposedly some performance number. What is this number? I could not find anything related with my search engine mojo ...
I think you are seeing the bisection width. An equal bisection is N1/2. You could also have something like N1/3 and N2/3. A bisection of N1/2 implies that there are an equal number of end-devices on each side of the bisection.
You bisect a network to look at the bandwidth over-subscription between the two sides. Ideally you want to be able to bisect the network and have a 1:1 ratio between the cumulative access bandwidth on one side with the bandwidth available to get the traffic to the other side. The problem with that is that it can be prohibitively expensive, or even impossible to achieve with the current network topology. The point is that you need to understand the over-subscription in order to take it into account and understand your network.