As far as I can tell, an edge stitch is an extra stitch that you slip at the beginning of every row (some people slip their edge stitches at the end of every row.) I'm not sure if there's any difference when you slip it knitwise or purlwise.
Edit: I would just like to note that according to my forum clock, Ingrid and I posted simultaneously. :P But it doesn't count seconds.
I'm a boy, by the way.
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