A product requirements document (PRD) is a document

Document

The term document has multiple meanings in ordinary language and in scholarship. WordNet 3.1. lists four meanings :* document, written document, papers...

 written by a company that defines a product they are making, or the requirements for one or more new features for an existing product. A PRD is often created after a marketing requirements document

Marketing Requirements Document

A market requirements document in project management and systems engineering, is a document that expresses the customer's wants and needs for the product or service.It is typically written as a part of product marketing or product management...

 (MRD) has been written and been given approval by management, and is usually written before (or at least concurrently with) a technical requirements document. It is designed to allow people within a company to understand what a product should do and how it should work. PRDs are most frequently written for software products, but can be used for any type of product.

A PRD should generally define the problems that a product (or product feature) must solve, but should avoid defining the technical solution to those problems. This distinction allows engineers to use their expertise to provide the optimal solution to the requirements defined in the PRD.

A PRD sometimes serves as a marketing requirements document

Marketing Requirements Document

A market requirements document in project management and systems engineering, is a document that expresses the customer's wants and needs for the product or service.It is typically written as a part of product marketing or product management...

 as well, particularly if the product is small or uncomplicated.

Components

Typical components of a software product requirements document are:

• Title & author information
• Purpose and scope
  Scope (project management)
  In project management, the term scope has two distinct uses: Project Scope and Product Scope.Project Scope"The work that needs to be accomplished to deliver a product, service, or result with the specified features and functions."Product Scope...
  
  , from both a technical and business perspective
• Stakeholder identification
• Market assessment and target demographics
  Demographics
  Demographics are the most recent statistical characteristics of a population. These types of data are used widely in sociology , public policy, and marketing. Commonly examined demographics include gender, race, age, disabilities, mobility, home ownership, employment status, and even location...
  
  
• Product overview and use case
  Use case
  In software engineering and systems engineering, a use case is a description of steps or actions between a user and a software system which leads the user towards something useful...
  
  s
• Requirements, including
  • functional requirements
    Functional requirements
    In software engineering, a functional requirement defines a function of a software system or its component. A function is described as a set of inputs, the behavior, and outputs ....
    
     (e.g. what a product should do)
  • usability
    Usability
    Usability is the ease of use and learnability of a human-made object. The object of use can be a software application, website, book, tool, machine, process, or anything a human interacts with. A usability study may be conducted as a primary job function by a usability analyst or as a secondary job...
    
     requirements
  • technical requirements (e.g. security, network, platform, integration, client)
  • environmental requirements
  • support requirements
  • interaction requirements (e.g. how the software should work with other systems)
• Constraints
• High level workflow plans, timelines and milestones (more detail is defined through a project plan
  Project plan
  A project plan, according to the Project Management Body of Knowledge, isPRINCE2 defines:In some industries, particularly information technology, the term "project plan" can refer to a Gantt chart or other document that shows project activities along a timeline. While common, this use is inaccurate...
  
  )
• Evaluation plan and performance metrics
  Metric (mathematics)
  In mathematics, a metric or distance function is a function which defines a distance between elements of a set. A set with a metric is called a metric space. A metric induces a topology on a set but not all topologies can be generated by a metric...
  
  

Not all PRDs have all of these components. In particular, PRDs for other types of products (manufactured goods, etc.) will eliminate the software-specific elements from the list above, and may add in additional elements that pertain to their domain, e.g. manufacturing requirements.

Levels of requirements definitions

The following words are used to indicate different levels of requirements:

• MUST - This word "MUST", or the adjective “REQUIRED”, or "MANDATORY" means that the definition is an absolute requirement of the specification.
• MUST NOT - This phrase means that the definition is an absolute prohibition of the specification.
• SHOULD - The word "SHOULD", or the adjective “DESIRABLE”, means that there may exist valid reasons in particular circumstances to ignore this item, but the full implications must be understood and carefully weighed before choosing a different course.
• MAY - The word "MAY" or the adjective “OPTIONAL”, means that this item is one of an allowed set of alternatives. An implementation that does not include this option MUST be prepared to inter-operate with another implementation that does include the option.

Another way to define levels of the requirements is by using the MoSCoW Method

MoSCoW Method

MoSCoW is a prioritisation technique used in business analysis and software development to reach a common understanding with stakeholders on the importance they place on the delivery of each requirement - also known as MoSCoW prioritisation or MoSCoW analysis.According to A Guide to the Business...

.

See also

• Marketing requirements document
  Marketing Requirements Document
  A market requirements document in project management and systems engineering, is a document that expresses the customer's wants and needs for the product or service.It is typically written as a part of product marketing or product management...
  
  
• Requirements management
  Requirements management
  Requirements management is the process of documenting, analyzing, tracing, prioritizing and agreeing on requirements and then controlling change and communicating to relevant stakeholders. It is a continuous process throughout a project...
  
  
• User requirements document
• Product planning
  Product planning
  Product Planning is the ongoing process of identifying and articulating market requirements that define a product’s feature set.Product planning serves as the basis for decisions about price, distribution and promotion.- See also :* Product planning...
  
  
• Product architect
• Product management
  Product management
  Product management is an organizational lifecycle function within a company dealing with the planning, forecasting, or marketing of a product or products at all stages of the product lifecycle....