What is a Progressive Elaboration?
Progressive elaboration is the principle that project plans get continuously more detailed and accurate as better information becomes available. You don't know everything on day one — and pretending otherwise produces confident nonsense. Plans are refined iteratively as the fog lifts.
Don't confuse it with scope creep: elaboration adds detail to existing scope; creep adds new scope. Rolling wave planning and prototyping are both progressive elaboration in action.
Worked example
An estimate for a machine-learning feature starts as "roughly one quarter, two engineers" at the business-case stage, becomes "11 weeks, broken into data pipeline, model training, and API" after discovery, and lands as task-level plans once a prototype proves the approach. Same scope, sharper picture each pass.