A stepped profile is a description of the height of a river above sea-level with distance from its source. A stepped profile when plotted on a graph would not show a smooth line showing decreasing height with distance from the source (this is a long profile). A stepped profile would show dramatic decreases in height - this may be caused by the type of underlying bedrock changing allowing the river to erode vertically,horizontally or diagonally
References
Stepped profile Wikipedia(Text) CC BY-SA