Graph theory what is a bottleneck (mathematics)

Hi guys,
I’m studying for my exam this week and I only have one question about graph theory that is what is a bottleneck and a matching? Because I don’t get it |S| >= |N(S)| Is a bottleneck but can someone explain please?
Kind regards,
Answer #1
hey ya go, mate.
I’ve done the research you should have done before you posted here
http://en.wikipedia.org/wiki/Bottleneck
here’s the first couple of lines from the articles which explain what the bottleneck effect is
A bottleneck is a phenomenon where the performance or capacity of an entire system is limited by a single or limited number of components or resources. The term bottleneck is taken from the 'assets are water' metaphor. As water is poured out of a bottle, the rate of outflow is limited by the width of the conduit of exit—that is, bottleneck. By increasing the width of the bottleneck one can increase the rate at which the water flows out of the neck at different frequencies. Such limiting components of a system are sometimes referred to as bottleneck points.
they are referring to all systems (mathematical, electrical etc) in that extract
Answer #2
Thanks but I already read that before posting it here wiki ftw. But I wanted a example on a graph that’s why I’ve posted the question here