What document outlines a web project's basic requirements including its purpose and audience?

The appropriate document that outlines a web project's basic requirements, including its purpose and audience, is the specification document. This document serves as a comprehensive guide that details the project scope, functionalities, and design elements, ensuring all stakeholders are aligned on what the web project aims to achieve.

While a storyboard is a useful visual tool for illustrating the sequence of interactions or the layout of the website, it does not encapsulate the high-level requirements and overarching purpose of the project like a specification document does. Similarly, a blueprint usually refers to architectural layouts and plans, which may not specifically pertain to web projects. A requirement outline can serve the purpose of documenting needs but lacks the depth and structure provided in a specification document that typically includes comprehensive details on target audience, features, and overall goals.

Thus, the specification document is vital in establishing a clear framework for the project's direction and is helpful for developers, designers, and stakeholders throughout the project lifecycle.