Define "thickness" as it pertains to aggregate base layers in construction.

Thickness, in the context of aggregate base layers in construction, refers to the vertical depth of the layer within the overall pavement structure. This measurement is crucial as it impacts the structural integrity and load-bearing capacity of the pavement. The thickness of the aggregate base is critical for determining how well the layer can distribute traffic loads, manage drainage, and provide an appropriate foundation for the layers above it.

Evaluating the thickness ensures that the construction meets design specifications, which directly influence performance and longevity. If the thickness is insufficient, it could lead to premature failure of the pavement, while excessive thickness may result in unnecessary costs and increased material usage.

Other options describe different physical characteristics or properties of the aggregate that are important but do not pertain directly to the definition of thickness itself. The width relates to lateral dimensions, the moisture content impacts compaction and stability, and density affects the load-bearing characteristics, yet none of these capture the specific concept of thickness as it pertains to the vertical measurement of the layer.