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From original question
I thought only " what does@@mean?"was grammatically correct but I heard a lot of Americans saying "what does it mean by @@?"
If you saw something confusing on a street sign, you might point and say "what does it mean by that".
Here, "it" would refer to the sign. You are treating the sign as if it were a person who had said something. So it's very similar to sentences like "What did he mean when he said that?"
This isn't particularly common. If you are reading and trying to understand a book that has a lot of confusing sentences and it's like the book itself starts to take on an evil identity...it might be more common. :-)
As for "What does it mean that (...)", there are rare cases you might hear it as a kind of question to provoke thought, where you're not expecting an answer (e.g. a "rhetorical question".)
- "What does it mean that one fourth of humanity lives without electricity?"
But if you're really asking about what something means, "What does (...) mean?" or "What's the meaning of (...)?" would be what you'd want to use.
From updated question
I thought only "what does _____ mean?" was grammatically correct but I heard a lot of Americans saying "what do you mean by _____?"
Are both of them correct? Are there any differences between those two?
If you ask "what do you mean by ____" then you are suggesting the person has said something you want them to explain. But "what does ____ mean" could be asked of someone whether they've said anything or not. You're just asking a question about the general meaning of something.
In usage, "What do you mean by that?!!?" can be a strong negative reaction...usually when someone has said something that the person feels was meant to be insulting even if it wasn't "obviously" so. So it's not really asking for clarification, because the speaker has already assumed it was meant in a bad way.
But it can also just be a polite phrase asking what someone meant.
Another variant might be that the subject is a quotation. For example, I might respond to part of your question by saying
What do you mean by "correct"?
The implication is that in order to answer your question, I need to understand what the quoted portion means to you in this context.
The use of that instead of a specific quoted part simply means the whole statement. As others have mentioned, the emphasis is on what the original speaker or writer meant.
(Note: I don't actually require you to tell me what you meant by "correct" in this case; I was just using that as an example)
I'm in a couple of group chats, and it's mostly fun banter and jokes. Sometimes the women will react with a ‼️to a comment. It could vaguely mean shock, surprise, frustration or offense. Or maybe to call attention to something they don't agree with or feel some kind of way about without saying it. I get the feeling that it never means anything good.
What exactly does it mean when women react with the double exclamation emoji in text? I've only seen women use it, none of the guys I know do this. So asking here.
'What's that mean?' translates to 'What does that mean?'—not 'What does it mean?'. I'd say that the phrase 'What's that mean?' is a dialect more than anything else, and even in informal speech, 'What does that mean?' is more common and more often understood.
One of the meanings of 's is "does" - this is often forgotten. We say that 's means "is" or "has" and forget that it can mean "does".
Some answers and comments wrongly regard this usage as incorrect or as dialect.
It is an informal usage but it is neither incorrect not dialectal. Lexico records it here https://www.lexico.com/definition/'s