The story
Coined by Leslie Kalbfleisch (a.k.a. Leslie Kay) in 2011 with her Tumblr blog called DisneyBound, from Disney + -bound. Kay described the context: “It was a travel site. My best friend and I were heading to Disney World, and we had been planning that trip since we were young … I was using this blog as a way to channel my excitement because we were literally Disney-bound. So I started doing these outfits, which is something that I always did when I was a little kid … I could dress up in these clothes without it actually being a costume.”
Etymology from Wiktionary, CC BY-SA 4.0.