When you are discussing the performance of a building’s foundation in the Houston area, you are normally trying to relate how well it is currently supporting the structure of the building over the expansive soil building owners deal with daily here.  The question asked by clients is always whether the foundation has settled.  What they really want to know is whether the foundation has settled differentially, which is the term used by many, if not all, engineers, and I believe is not well understood by some buyers or owners.  In reality, for the purpose of structural performance, most people probably don’t care much if a foundation simply settles which implies it is moving down in a uniform manner.  Uniform settlement implied by the term, “settlement”, typically does not result in damage to the supported structure.  Owners do get very upset if a part of the foundation settles while another part does not, which is what is meant by the term, “differential settlement”.  A foundation that has settled unevenly across the projected area of the soil which supports it has settled differentially.  This can result in bending and deflection of the structure supported by the foundation, which can be devastating to a building.  Most recommendations for maintenance and some methods of repair or reinforcement relate back to the need to prevent differential settlement.