Mass media use the term 'stair-stepping' when they can't explain the
computer graphics concept of
aliasing.
In computer graphics, images are typically drawn in raster format; squarish pixels are filled with colors in much the same way that cross-stitch patterns are. Your screen is in raster format, with hundreds of thousands of pixels.
To draw round objects with squarish pixels, the computer or artist must make choices between two colors (aliasing) in jagged stair-steps, or use additional colors partially between the two (anti-aliasing).