Professional Development Units (PDUs) are a measure used to quantify the time and effort invested in professional development activities. They are often required for maintaining certifications in various fields, such as project management or education. One PDU typically represents one hour of learning or professional service. PDUs can be earned through various activities, including attending workshops, completing online courses, or participating in conferences. Organizations like the Project Management Institute (PMI) provide guidelines on how to earn and report PDUs, ensuring that professionals stay current in their fields and enhance their skills.