CAP is the abbreviation for Community Acquired Pneumonia and is used to define pneumonia that develops within 48 hours of admission to hospital.
HAP is the abbreviation for Hospital Acquired Pneumonia and defines pneumonia that develops > 48 hours post admission to hospital. It is also called nosocomial pneumonia.
VAP is the abbreviation for Ventilator Associated Pneumonia and is a form of HAP. It is used to define pneumonia that develops > 48 hours after the onset of mechanical ventilation, and up to 48 hours following termination of ventilation.