Knit 1, yarn over, knit 1, yarn over, knit 1 increase: (k1, yo, k1, yo, k1) all in the same stitch
This tutorial explains an increase method that involves working multiple stitches in a single stitch. A (k1, yo, k1, yo, k1) all in the same stitch is a quadruple increase, working 5 stitches in one stitch, for a net gain of 4 stitches.