A bottleneck may refer to any of the following:
1. A bottleneck happens when too much data enters one source and causes a computer or network to slow down or become unresponsive. For example, a website could be mentioned on a popular page that causes a bottleneck because of all the traffic sent to the web server. In this bottleneck example, the visitors trying to visit the website would encounter errors or unusually slow load times.
A real-life good example of a network bottleneck was on September 11, 2001. On this day, terrorists coordinated four attacks across America. So many people were trying to visit online news sites at the same time to find out more about the attacks that most of the sites became unresponsive or took several minutes to load.
2. A bottleneck is also the weakest or slowest stage of a program or algorithm.