In short
HAZOP is a risk analysis method that systematically examines deviations from a process's design intent using guide words to identify hazards and operability problems.
A multidisciplinary team goes through process flow diagrams node by node, using guide words such as more, less, none and reverse to discuss possible deviations, causes, consequences and existing safeguards.
It is common in chemical and energy plants. Tracking HAZOP actions with owners and due dates determines the value of the study.