I'm not up to date on _*Equestria Girls_* either, and I'm just not good with finding names. I imagine the very first outfits the characters wore in the titular first movie would have "original" somewhere in the tag and that's it.
I do know that "[rarity peplum dress":](/tags/rarity+peplum+dress) is a thing though (along with "[rarity's peplum dress":](/tags/rarity's+peplum+dress), which may call for merging or aliasing), so there's precedent for giving Rainbow's singing dress its specific tag. And _*some_* demand, presumably. Dress seems popular, at least from the comments I got.
**Edit:** Speaking of [this version](/images/2198672) of Rainbow Dash, I've been stumped on something for a long time. Is she sporting a [braid](/tags/braid) or a [headband](/tags/headband)? Seems pretty clear to me that she's braided her hair, what with the way it looks and the matching colors, but [headband](/search?q=spring+breakdown%2Crainbow+dash%2Cheadband) gets roughly three times as many results as [braid](/search?q=spring+breakdown%2Crainbow+dash%2Cbraid); including my own picture, which is what made me notice this in the first place.
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Another inquiry. I was browsing "equestria girls,armor" when _*these_* showed up.
>>2406344s >>2397992s
...Am I missing something? Or should I go and remove the "[armor":](/tags/armor) tag?
Ah, and as someone who keeps harping on you all about descriptions, I appreciate the very detailed one for "[solo female":](/tags/solo+female). I was confused as to why the second image didn't have that tag, but then I noticed "For safe-rated images, please just use "[solo":](/tags/solo) instead." Thanks for the preemptive clear-up!