Requirements are the information that best communicates to an engineer what to build, and to a quality-assurance manager what to test.

A requirement has three functions:
• Defines what you are planning to create
• Identifies what a product needs to do and what it should look like
• Describes the product’s functionality and value

Requirements vary in complexity. They can be rough ideas sketched on a whiteboard or structured “shall” statements. They can be text, detailed mock-ups or models, and can be part of a hierarchy with high-level requirements broken down into sub-requirements. They may also be detailed specifications that include a set of functional requirements describing the behavior or components of a product.

High-level requirements are sometimes referred to simply as “needs” or “goals.” Software development practices might refer to requirements as “use cases,” “features,” or “functional requirements.” Agile development methodologies often capture requirements as “epics” and “stories.”

Regardless of the terminology, requirements are essential to the development of all products. Without clearly defining requirements, companies risk creating incomplete or defective products.

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