In a bottle of water, there is a literal bottleneck at the top where the large space of the bottle narrows to fit someone’s mouth.

The four lanes of traffic became a major bottleneck when the highway changed to just two, slowing down everyone.

There is a bottleneck where the ocean flows inland, transforming into a much smaller river as it hits the coast.

The collar of a shirt is technically a bottleneck, where a very large amount of space becomes a much smaller one to comfortably fit the neck.

There is a bottleneck in the mall up ahead, because everyone on this floor that wants to go to the next only has one escalator to use.