I recently received an invitation to join the Yahoo Requirements Engineering Group. This led me to thinking about my definition of a requirement. I saw a similar definition in a document (it was part of the boilerplate text) delivered by a consultant at a prior position. It was the most useful item in the document… (For the life of me, I cannot remember who the consultant nor firm was.)

Requirement – A testable assertion of a customer’s need.

I like this definition a lot because it is simple and lacks a lot of the technical jargon or background knowledge required for other definitions. The terms are understandable by business users. The one thing I always add when I deliver this definition is that customer is not limited to our external customers – it is inclusive of all our internal customers.