"rib knit" (also frequently called ribbing) is a basic knitting stitch pattern. In short, you alternate knit and purl stitches, aligning them vertically to form columns. Ribbing is very stretchy and frequently used for cuffs or other places you want a snug fit. You can view a video of making ribbing here
. The number designation (2x2, 3x3 etc) indicates how many knit and purl stitches make up each vertical column. In this pattern, which calls for a 2x2 rib, you will alternate two knit stitches and two purl stitches.
Hopefully that answered your question. If not let me know and I will try to elaborate further. Good luck and happy knitting! xxx