When I started using this term, I had no idea that it stood for something in Aspie Supremacy. I knew I had ADHD before I knew I was autistic. I was diagnosed in 1988 as severe ADHD and language receptive/expressive disorder.
I found facebook groups for autistic adults. It is used often in the adult ADHD community. I loved it, adopted this and my children use it often. My kids use the term as well. It is used as an Identify First Language term. It is to poke fun that we are easily distracted. You could see a butterfly in the window that belongs to the classroom across the hall. This would catch your attention. Something "shiny" could be anything that catches your attention. It does not have to look shiny to be shiny. This is to say "ooh shiny!" Its a way of poking fun at ourselves and not saying we are diseased.
Later, after I found out I am autistic, I found out that the Aspie Supremacists like to use the term "shiny aspie." This made me sad. I am the furthest thing from a supremisist. I identified as shiny due to my ADHD. In no way is it meant to have a supremacy or superior undertone. I do not want to stop using this term. There are two meanings to it.
Other terms used: Shiny Chicken, Squirrel (due to a dog's reaction to a squirrel), chicken (they are easily distracted too!).
I hope that answers any questions that anyone may have about the Shiny term for ADHD.