OECD Releases “Education at a Glance 2021”

It's not exactly an obscure term. I didn't know what it stands for, but it's very, very common to refer to "OECD countries", so I knew it was more or less synonymous with "developed Western countries".

Looking over the membership list, it also includes Japan, Korea, Turkey, and several Latin American countries.

By "dig into footers", you mean scroll to the bottom of the page where it shows the full name just like most corporatey sites do? What would be better? Spelling it out in the title where almost nobody visiting it would gain any value from it because why are they there if they don't even know what it is? What even is the use of knowing what the acronym stands for? It's barely any more meaningful than the 4-letter name.

I get what you're trying to say but OECD isn't exactly an obscure organization, it's as common as NATO, UNICEF, or IMF.

I wouldn't be surprised if more people knew of the OECD than IEEE.