CAPM
Certified Associate in Project Management
Project Management Institute
What stuck
The framework for thinking about scope, schedule, and cost trade-offs has been useful in client conversations, and the explicit vocabulary for risk registers and stakeholder analysis is something I reach for repeatedly.
What didn't
The PMI-specific terminology rarely matters outside formal PMI environments; I translate to plain English in practice. The detailed mathematical formulas for EVM I have not used since the exam.