Ah, textile terminology is a thing to talk endlessly about - or maybe I should say "whine endlessly about"? And it gets even worse when things get translated.
One of the common problems concerns buttonholes (or lacing eyelets, in the time before the buttonhole's rise to prominence). There are three different stitches that can be used for securing the edge of eyelets or slits: the basic overcasting stitch (whip stitch), blanket stitch and buttonhole stitch. And the last two have a history of being confounded with each other, and often both types are called "buttonhole stitch". But there is a difference!
For a whip stitch, the needle enters the fabric from the front side only, and this results in the thread spiraling through the fabric, around the edge, through the fabric and so on. Whip stitch is technically able to do the job around an eyelet or buttonhole, but I can't really remember any extant example - and blanket stitch is nicer to work than whip stitch around those kinds of edges.
For a blanket stitch, the needle goes in at the front of the fabric, out at the back, but in addition, on the way back to the front for the next stitch, the needle is going through the loop that forms around the edge of the fabric. This forms a continuous line of thread lying more or less on top of the edge, thus protecting it better than simple whip stitch. (You can see blanket stitch in a stitch dictionary on this page - scroll way down.)
For a buttonhole stitch, the needle also goes through the loop after going through the fabric, but from front to back. This forms a little knot (a half-hitch, in effect) that is supposed to sit right on the edge of the fabric. This, if made accurately, will hold the continuous line of thread even better on top of the fabric edge.
So what are the differences? Buttonhole stitch takes a little longer to work than blanket stitch (at least for me), because in the way that I make it, I need to change my hold on the needle one more time per stitch (for forming the knot). What takes more time, though, is to make sure the little knot is placed and tightened correctly, and this can be fiddly work.
The biggest difference, however, is discernible when working the stitches tightly beside each other, as required in eyelets or button holes. Then it becomes evident that buttonhole stitch will build up on the edge, effectively making the hole a little smaller. This is not too bad on a buttonhole - in fact, it might even help countering the buttonhole's tendency to widen with use, but on an eyelet hole that is only poked into the fabric and not cut, it's much better to have it in the same size after finishing it. And I have not yet found a true buttonhole stitch in medieval context - this seems to be used only in modern times.
And the conclusion? When I read a term for a stitch, I always look for a picture of the stitch in question - because you can never be sure which terminology the author uses. And when I name a stitch, I always try to give an additional description or picture - because it's never a given that everyone else will think of the same stitch as I do when I name the name.