YO-SD is short for Young Super Dollfie
Be careful about 26cm dolls - some are like Barbie and other fashion dolls, others are the same height but meant to be very young children. This can cause trouble when you see a wig you love and it's labeled for 26cm dolls. It's much better to go by the head size. For example: A 1/6 obitsu usually has a head that is 3 to 4 inches around. They take wig sizes 3/4 (which stands for three to four and not three quarters). My Dollzone Juli, who is also 26cm, is a young child doll. His wig is 6/7 (for six to seven inches). Always double check your measurements. And ask questions! We have all been there! I thought I would never understand it all, and now I find myself knowing exactly what company and sculpt a doll is fairly often!
If you can go to a doll meet, you can actually get to see them in person. That is a really good way to learn.