A loop (yarnover) that gets put onto your needle accidentally. A yarnover makes a lacy hole in your knitting. If this is not wanted, make sure to catch it and remove it as soon as possible.
How to Fix Mistakes in Ribbing
Unraveling your knitting (usually entirely). Frogging gets its name from what you do when you unravel: “rip-it, rip-it.”
To “un-knit,” i.e., undo your knitting stitch by stitch. The work “tink” gets its name from “knit” spelled backwards.