In Microsoft 365 Copilot, a notebook is a workspace intended to organize and ground related Copilot work. Microsoft guidance describes notebooks as a way to bring together multiple conversations and keep them aligned to the same set of reference materials—such as documents, notes, links, or other resources—so you don’t have to repeatedly attach or restate the same context. This improves consistency and prompt-grounding across a set of related tasks (for example, managing a project, developing a proposal, or maintaining a recurring report).

Option B correctly captures this purpose: a notebook provides a private, organized location where reference materials can be curated and reused across related Copilot conversations.

Option A is incorrect because notebooks are not primarily designed to generate email-ready transcripts of conversations. Option C is incorrect because generating a summary of interactions is a conversation-level function; notebooks are broader organizational containers for materials and related workstreams, not a “summary generator” of a single chat thread.

Therefore, the purpose of a notebook is to organize reference materials across related conversations.