“Soft story” describes any part of a building that has  a living space above an open basement and multiple windows side by side, or above a two-car garage, porch, or carport that was not specifically designed to transmit shear lateral force to the story above (i.e., remain secure during an earthquake). 

Specifically, split-level houses and other homes with a living space over a two-car garage are at special risk of having the living space collapse into the space below during severe earthquake shaking. 

Multi-family apartments and condos with large, open parking areas on the ground floor are also at considerable risk of collapse into the space below during an earthquake. 

The "ABCs of retrofit" (anchoring the foundation, bracing walls, and connecting flooring with metal clips) still apply for buildings like these, but additional engineering design is required to minimize the risk of collapse for the "soft story" area.