Glossary: repeat(s)(ing)
rep = repeat(s)(ing)
It is the abbreviation for 'repeat', meaning 'do it again'.
A typical usage of this would be 'Rep Rows 1 - 8 until item measures 8 inches'.
Another usage is to put a special character like a '*' into the pattern and then state 'rep from * x times' meaning that you should find the '*' mark and repeat all stitches from that point for the number of times indicated.