Which axis is referred to as the 'abscissa' in a graph?

In the context of a graph, the term "abscissa" specifically refers to the horizontal axis, which is the X-axis. This terminology comes from coordinate geometry, where the abscissa indicates the distance along the horizontal direction from the origin (the point where the X and Y axes intersect) to the point in question on the graph.

Understanding this terminology is important when interpreting graphs, as each axis represents different dimensions of the data being analyzed. The X-axis often represents the independent variable, while the Y-axis (known as the "ordinate") represents the dependent variable. This distinction is crucial in various fields, including statistics, as it helps clarify the relationships and changes between the variables being examined.

The other options do not accurately describe the abscissa; the Y-axis refers to the vertical direction, the start point of a graph is not a defined term in this context, and the Z-axis pertains to three-dimensional graphs, which is outside the scope of the traditional two-dimensional representation where the concept of an abscissa applies.