Bias knitting is a method by which the grain of a knitted fabric is skewed from the vertical, by decreasing on one side and increasing on the other. The term "bias" derives from sewing, where bias refers to the diagonal between the weft and warp threads, where the elasticity of wovens is greatest.
A classic use of bias knitting is in making a saw-toothed knitted hemline for a garment, with a central double decrease flanked by single increases on either side.
References
Bias knitting Wikipedia(Text) CC BY-SA