The term “bottleneck” originally comes from the shape of a bottle. Think of a bottle: it has a wide base where you can hold a large amount of liquid, but as it narrows toward the neck, the liquid slows down because there’s less space. This narrow point where the flow is restricted is what we call the “bottleneck.”

In the context of English idioms and expressions, “bottleneck” came to mean any situation where progress or flow is slowed down by a restriction or obstacle. It’s commonly used in areas like business, technology, and traffic to describe a part of a process where things get delayed or held up.

For example:

• Traffic bottleneck: A narrow or busy section of a road where cars pile up, slowing down traffic flow.
• Project bottleneck: A step in a project that slows down overall progress, like waiting on a critical approval.