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.