Oracle used to do that, didn't they?

So, amongst others, they had Oracle 8i at the height of the dot com boom (i for "Internet"), then a few years later when clustering became big news there was Oracle 10g (the g standing for "grid", I think?), and so on.

Actually, it looks like they might still be doing it - I just checked, and their current version is 23ai...

Exactly.

There's nothing specific about the letters after Oracle's RDBMS versions, they're for marketing purposes.