The traditional business plan used to be a 200 page Microsoft Word document. A large part of it was filled with fluffy market background information and more fluffy industry buzzwords, frameworks and mission statements. It was always out of date. Its primary purpose was to rest your hand on it and say: “We have a business plan”. Nobody would really read it.
In most startups, the business plan is replaced with a large PowerPoint slide deck that evolves rapidly over time. A selection of the slides in this document are upgraded to be used in standup presentations. The vast majority of them are dense appendix material.
Daniel Tenner wrote a good blog post about what it means when an investors asks whether you can email her a business plan. In short, after the initial pitch, the investor wants a document that can be emailed (forwarded to partners) that answers some fundamental questions about your venture. The content should be good, the content can be short, and you can afford to invest less in the design of the slides.