Concept development is the first creative phase of any design project — before drawings, specifications, or shopping. The output is usually a concept document or moodboard plus a written rationale that captures: what this project is fundamentally about, what it should feel like, what its references are, and what it deliberately is not.
Professional designers spend more time here than amateurs expect. The concept is what every later decision will refer back to: when comparing two sofas, you ask which one fits the concept; when choosing paint, you ask which color the concept supports; when budget tightens, you cut what doesn't serve the concept rather than uniformly cheapen everything.
AI tools have shifted concept development for consumers. Where concept work used to require designer time, today you can iterate through AI-generated mood boards in an evening, narrow to a direction, and commit before any spend.