The phrase 'in a nutshell' means to summarize something in a brief and concise way, providing the essential points without unnecessary details. It is often used when someone wants to convey the main idea or conclusion of a story or explanation quickly.
The phrase 'in a nutshell' dates back to at least the early 17th century. It is believed to have originated from the idea that something small, like a nutshell, can contain something much larger or more significant, akin to how a brief summary can encapsulate a larger concept.