Not a stupid question, it had me puzzled for awhile too.
ETA meand “edited to add…”
SS ETA I see that in the time it took me to type that three others answered the question!
Edited to add. It’s not on the faq since it’s a vaguely recent term, since post editing has only been here for a few years now and the faq gets updated maybe once a decade. Basically it’s a postscript of sorts.
The advantage of identifying something with “ETA” is that if someone reads your post before you edit it, they can see at a glance what you’ve added. It’s a bit academic here because the edit window is so short, but on other forums I think it can make for easier reading. I guess it’s also a sort of courtesy to people responding to your post, in that it makes clear that their “failure” to respond to something you’ve said is because it wasn’t there when they themselves posted.
Yeah. The other reason I try to remember to use it in various heated debates is to make it clear why I was editing, so that it doesn’t look like I had a change of heart about an insult or something. There’s the ‘reason for editing’ bit at the bottom, but it’s too small for adding actual content.