What is defined as the angle that subtends exactly 100' of arc length along a circular curve?

The angle that subtends exactly 100 feet of arc length along a circular curve is defined as the degree of curvature. This term is specifically utilized in surveying and civil engineering to describe the curvature of a circular path. It provides a standardized measure of how sharp or gentle a curve is by identifying the relationship between the angle and the arc length.

In more technical terms, the degree of curvature is calculated as the angle in degrees that corresponds to an arc length of one hundred feet. This measurement is crucial in the design of roads, railways, and other infrastructure that involves curvilinear paths, as it assists engineers and surveyors in ensuring appropriate turning radii for vehicles and maintaining safe travel conditions.

The other choices, while related to the field, do not accurately define the concept at hand. A fillet refers to a rounded corner or edge, often relevant in design and architecture. A segment relates to a portion of a curve, specifically in a circle but does not convey the angle-to-arc length relationship. Slope describes the incline or steepness of a surface or line, not a property of circular curves.