A core tenet of modern development processes is agile development. This development methodology stresses using small, bite-sized user stories to define what a system does from a user perspective, not a technical one. A user cares if a product is fast, easy to use, and solves their problem. They do not care if it follows a 3-tier architecture, has Mongo DB, or if it is using Rails or Asp.net.
Be as specific as possible in describing the prototypical user(s) of your product.
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Carl the Customer
Carl has a college degree and has been working for 7 years. He likes technology but worries about the cost of new widgets. In general he is a nice guy, but his patience is short right now.
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Angie the Agent
Angie has a college degree and 4 years of work experience in customer support, her second career. She is good with basic computer applications, like Office, and surfs the web a lot in her free time.