Great question! The term skinny jean has changed over time. What I could have been more careful in defining is what a "modern skinny jean" is: it is designed t

Great question! The term skinny jean has changed over time. What I could have been more careful in defining is what a "modern skinny jean" is: it is designed to be form fitting throughout the seat and leg. That means a tapered leg opening: the knee is larger than the hem. That also means the garment measurements are smaller than your own body measurements everywhere, except possibly at the leg opening. Lycra/spandex/elastane had been incorporated in jeans in the 60s (I checked the Sear's catalogue to verify material composition when I was researching this), but the jean silhouette of the pants they sold were closer to what we'd call a "slim fit" today. Same with denim in the early 1970's: it hugged the body, but wasn't skin tight everywhere, and often was boot cut at the leg opening. Fiorucci was the first to add stretch to denim with the purpose of making the jeans skin tight and tapered at the leg.