Business requirements are often listed in a Business Requirements Document or BRD. The emphasis in a BRD is on what is required, rather than on how to achieve it, which is usually delegated to a Systems Requirements Specification (SRS) or other variation such as a Functional Specification Document (FRD).
Business requirements in the context of software engineering or software development life cycle, is about eliciting and documenting business requirements of business users such as customers, employees and vendors early in the development cycle of a system to guide the design of the future system.
Business requirements are often captured by business analysts, who analyze business activities and processes and often study As-is process to define a target To-be process.
Business requirements often include
Business context, scope, and background, including reasons for change
Key business stakeholders that have requirements
Success factors for a future/target state
Constraints imposed by the business or other systems
Business process models and analysis, often using flowchart notations to depict either 'as-is' and 'to-be' business processes
Logical data model and data dictionary references
Glossaries of business terms and local jargon
A software requirements specification (SRS) is a description of a software system to be developed. It lays out functional and nonfunctional requirements, and may include a set of use cases that describe user interactions that the software must provide.
Software requirements specification contains what the software product is to do as well as what it is not expected to do and these are called functional requirements.
Functional requirements are supported by non-functional requirements (also known as quality requirements), which impose constraints on the design or implementation (such as performance requirements, security, or reliability).
Generally, functional requirements are expressed in the form "system must do requirement", while non-functional requirements are "system shall be requirement". The plan for implementing functional requirements is detailed in the system design. The plan for implementing non-functional requirements is detailed in the system architecture.
Software requirements specification permits a rigorous assessment of requirements before design can begin and reduces later redesign.
A Product Requirements Document (PRD) is a document containing all the requirements to a certain product. It is written to allow people to understand what a product should do.
A PRD should, however, generally avoid anticipating or defining how the product will do it in order to later allow interface designers and engineers to use their expertise to provide the optimal solution to the requirements.