What does ETA mean? And, why use?

I noted that when you have edited a post it is recommended you add ETA.

What does the acronym mean?

Why use it?
Does it tell the search engine to look for an updated post?
Or, is it meant to tell those reading the post that they should refresh the page to see the updated post?

Please advise.

It means "Edited to add" and is considered a courtesy to let people know that the contents have changed since it was originally posted. This is very helpful when subsequent posts refer to things that are no longer in the original, edited post.

The acronym means "Edited to add".

It's a courtesy to readers, to let them know how the post differs from the original. This is especially important when there have been replies to the post prior to the edit. Consider the case when a poster omits an important detail, someone asks about it, and the original poster edits to add it in - to a later reader, it makes the questioner look like an idiot if the OP doesn't clarify that it wasn't in the original.

>1 Bettesbooks: Are you trying to shame us for using it?!?

ETA: Ah, now I understand that you are just curious. Sorry!

See >4 anglemark: for an example of usage.

I thought ETA was Estimated Time of Arrival hehe

>6 ScarletBea: That's what it means when I'm waiting for my latest book order. Hahaha.