In my opinion there are no structural cracks, just cracks in drywall, concrete, lumber, etc., which is a symptom or indication something has occurred. It could be from lumber shrinkage, foundation settlement., wind, earthquake, tree falling on the house, etc.
Structural damage is defined as any damage that compromises or affects the core integrity of your home . This includes the foundation, walls, roof and load-bearing walls. When significant damage occurs, the structure itself may be no longer able to support the house. The home may be in danger of collapse. For example the basement wall has two basic functions, transfer the house loading to the soil and act as a propped cantilevered retraining wall to hold back the soil. An 8-foot basement wall that is tipped in 1/2 inch is not a structural problem, just and indication the wall may be under designed or poor exterior grading or poor soil, etc. Once the wall has tipped in where the center of gravity is outside the middle third, then the wall has technically failed to hold back the soil. If you see cracks just describe them as small, large, diagonal, vertical, etc. unless you have all the puzzle pieces to know for sure its due to settlement, termite damage, wood rot, etc. Using the word structural to describe cracks is not appropriate IMO when dealing with non technical people like your clients and agents.