Stepped interpolation maintains the same keyframe value between keyframes. There is no slope between keyframes with Stepped interpolation.

Stepped interpolation A. Stepped interpolation mode selected B. Step interpolation option C. Stepped Step interpolation D. Step Next is the selected interpolation option E. Stepped Step Next interpolation

When Stepped is selected in the Interpolation Mode menu, the Interpolation Options menu lets you select Step or Step Next. These options are the same as those available when Stepped is selected as the interpolation mode in the FCurves window. See Step option and Step Next option for information.