The "gore" is usually a triangular shape inserted into patterns, like above a thumb in a mitten, but in the ptn for the slippers, they must have meant the somewhat triangular shape (lengthwise) formed when pulling the yarn tighter.
The Phentex slipper pattern didn't actually state "how" the puffy ridge was formed while knitting, clearly, if at all.
The ptn at woolworks is an old ptn, and it is closer than the Phentex ptn. (It didn't TELL how to actually "achieve" the formed ridges clearly, or much at all.)
The whole trick is to pull the yarn tighter, when knitting, when changing colors. "That" forces the knitting to pull together, THUS forming the ridge!
I'm a licensed instructor for knit & crochet (have done both for 54 yrs, since I was 7) and I have an old pattern like the Phentex slippers but I reformated, rewrote it totally and renamed it "Wrong Way Slippers" many years ago, when my adult children were babies. I named it "Wrong Way" because you PULL the threads tighter than you're supposed to, (thus being wrong) to "produce" the ridged "puffs".
Plus, I haven't seen ANY ptn for these slippers say to make them NON slip for little kids slippers on slippery wooden or any hard floor.
I use "Puffy" paint sold at craft stores. (Used for fabric painting T-shirts, etc.) I squiggle a line on bottoms of the completed slippers, allow to dry, then hold a med to hot iron CLOSE but NOT touching the bottoms of the slippers to "PUFF" the paint. (It automatically puffs up once heat is near) It poofs the paint out in a rubbery dimensional form. It makes a non slip bottom on the slippers, that lasts for many washings, for kids AND adults. Knit or crocheted slippers on wood floors are very dangerous!
PS I have seen tea cozy's made from this stitch technique, and also "Corn on the cob" pan handle covers! (It makes perfect rows of corn!) You have to either use "2" colors of yarn to keep pulling the "other" strand too much when you change colors, or two strands of the "same" color, to achieve the "ridges"...)
I hope this helps, I joined to answer the questions!!!! You can email me for more info. I hope I did the reply right! I'll look for my pattern to send you all if you want too.
Sleepless in Seattle, Tambo Knitpkr (Knit Picker)