Short rows are partial rows. Instead of working an entire row, a portion of the stitches in a row are worked. Multiple rows are worked to create shaping.
Short Row Shoulder Shaping
Short rows for shoulder are worked over a decreasing number of stitches. The number of stitches on the needles doesn’t change, just the number being worked. Extra rows are piled up where stitches continue being worked. Stitches are wrapped to prevent holes and the wraps are picked up and worked with stitch to hide them.
There are many ways to knit short rows, including s-w-s (slip, wrap, slip), and the German short row, both of which I’ve outlined here.