What is the difference between yarn over and yarn forward?
Here is a really good article about yarn overs, all you ever wanted to know and maybe more. Many times they are the same thing. But they can be something different. If you moved the yarn to the back for some reason and they just want you to move it back to the front and the next stitch happened to be a purl of some sort then there would be no YO. LINK to YO article.