# 16 of them stay the same, some of the rest are "questionable"

What do I call these?

Arranged in order:

       |   |   |   |   |   |   |   |   |   |   |
8↑          7↑      9↑
13↑
14↑

━   ━   ━   ━   ━   ━   ━   ━   ━
6↑      2↑
5↑
10↑
12↑
15↑

? 2 ? ? 5 6 7 8 9 10 ? 12 13 14 15 ? ?

• No knowledge (besides very trivial) is required Commented Aug 11 at 12:41
• Why did this puzzle get a downvote? It’s really smart
– PDT
Commented Aug 12 at 8:03

You call these...

REFLECTIVE LETTERS

Note that in this puzzle we have 11 vertical bars and 9 horizontal dashes. The trick is to realise (through experimenting and application of the title) that...

...there are 11 letters of the English alphabet that when capitalised are vertically symmetrical (i.e. their left and right halves are reflections of each other), and 9 letters that are horizontally symmetrical (i.e. their top and bottom halves are reflections of each other). These numbers match the numbers of appropriate corresponding symbols.

When pooled together, these two sets comprise 16 letters which "stay the same" (as per the title) when reflected along one axis or the other (or indeed both).

If we replace the bars and dashes with these letters, in alphabetical order, we get an image that looks like this:

On the top row we have: A, H, I, M, O, T, U, V, W, X and Y (the vertically symmetrical letters).
On the second row we have: B, C, D, E, H, I, K, O and X (the horizontally symmetrical letters).

Note now that there are various numbers with arrows pointing to particular ones of these...

If we substitute these letters in to the numeric sequence below it, we get:

? 2 ? ? 5 6 7 8 9 10 ? 12 13 14 15 ? ?
? E ? ? E C T I V  E ?  E  T  T  E ? ?

Using this, we can now...

enter unused letters (those without a line of symmetry) into the remaining question marks to give us a relevant term that can be used for letters with the property highlighted in this puzzle: rEflECTIVE lETTErs!

• Indeed that's what I call them, great job! :) Commented Aug 12 at 8:14