I am working on a pattern for placemats from a page-a-day calendar. It is basically a seed stitch border with a basket weave interior. There is a stitch separating the borders from the interior that in the picture of the FO looks like yo and k2tog, so it looks like one row of lace. The pattern says for this row to do "yf k2tog". There was a key with the calendar that lists abbreviations, and for yf it says "yarn forward: move yarn to the front of the work by going between the needle tips". I can't find this in any of my books. There is a separate definition for yo, so I don't think that's what they mean. Also, this pattern is started after 5 stiches, the last of which is purl, so the yarn is already in the front.
Can anyone explain to me what yarn forward is and how to do it? Thanks!