What does the term 'shear strength' refer to in soil mechanics?

The term "shear strength" in soil mechanics specifically refers to the maximum resistance of soil to sliding or deformation. It is a critical property that defines how strong the soil is in terms of withstanding forces that may cause it to fail or move. Shear strength is influenced by several factors, including the soil's cohesion, internal friction, and the effective stress acting on it.

Understanding shear strength is vital for various engineering applications, such as designing foundations, assessing slope stability, and evaluating the behavior of soil under loading. As such, it provides essential information about how soil will behave when subjected to forces that try to cause it to slide or deform.

The other options relate to important soil properties but do not define shear strength. Retaining moisture pertains to soil water retention capacity, weight per unit volume refers to soil density, and compressive strength specifically describes how well soil can resist compression, which is not the same as resistance to shear deformation.