Stage 03 of 5 · PDLC: Definition
What is the Define stage?
By Heemang Parmar · Updated July 2026
Define is the definition stage: research and concept become a structured product requirements document with scope, user stories, and success metrics, the source of truth every later stage reads.
Definition is where ambiguity goes to die. A good PRD settles scope disputes before they start and gives design and engineering something concrete to build against; a bad one just relocates the arguments downstream where they cost more.
In ProductOS, the PRD Agent writes the document section by section behind an outline-approval gate, grounded in the actual ideation and research artifacts rather than invented from scratch. Four templates cover different situations: ProductOS Standard, Amazon PRFAQ, Lean, and Enterprise. The optional Architect Agent extends Define with system architecture, ADRs, and infrastructure cost estimates.
Which agents run the Define stage?
How does the Define stage work?
- 1Outline approval: You approve the document outline before any section is written.
- 2Section by section: Each section is written against the research and concept, one deliverable per pass.
- 3Architecture (optional): The Architect Agent adds system design, ADRs, and cost estimates when the build warrants it.
- 4Handoff: The approved PRD becomes the source of truth the Design stage reads.
What does the Define stage produce?
- A sectioned PRD with user stories and success metrics
- An executive summary and revision-safe targeted edits
- Optional: architecture sections, ADRs, and cost estimates
Frequently asked questions
Which PRD template should I use?
ProductOS Standard fits most products. Amazon PRFAQ works when you want to pressure-test the narrative first, Lean when speed matters more than completeness, and Enterprise when compliance or regulated requirements apply.
Can I edit the PRD after it is approved?
Yes. Revision mode makes targeted edits to specific sections instead of rewriting the document, so an approved spec stays approved except where you changed it.