Music theory question: does anyone know what these diagrams are and what they're used for?

I keep seeing them around while researching music theory stuff on the net,
Especially when looking up chords

[image/video deleted]

It looks like it could be useful 🤔

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Gangstress · 41-45, F

It's good for major and minor chords

Gangstress · 41-45, F

@Harmonium1923 that's why i put think lol

helenS · 36-40, F

@Harmonium1923 Yes, and the A#-C#-E-F# thing doesn't make sense; it's not a chord. Two minor thirds and a major second on top of that??

helenS · 36-40, F

@helenS Oh!! It's F#-A#-C#-E, so ==> F#7

helenS · 36-40, F

The thick quadrilateral is apparently a C7 chord, but I don't get the thin one. 😐

WandererTony · 56-60, M

https://en.wikipedia.org/wiki/Chord_substitution

helenS · 36-40, F

@WandererTony Wow!! 🌷🌷🌷🌷🌷

WandererTony · 56-60, M

@helenS You could have clubbed those roses / tulips into a bouquet for me 😍

Gentlequill · 51-55, M

It's the devils mark! Oh lawd save us awl!!

Fishy · 36-40, F

@Gentlequill *pending joke about tritones*

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