Does it mean yes, or does it mean no, or something else?
Russian 'да' and 'нет' do not mean what English 'yes' and 'no' mean. English is somehow unusual as for the meaning of its 'yes' and 'no', as compared to other languages. In this respect Russian is closer to Japanese, than to English.
Russian 'да' means "I agree with what you say, you are right", Russian 'нет' means "I disagree with what you say, you are wrong", while English 'yes' means "What you say reflects the actual state of things" and English 'no' means "What you say does not reflect the actual state of things." On the surface, there may seem to be no difference between the approaches of the two languages, but, actually, that is not so. In Russian, if I ask you, "Ты его не знаешь?" and you answer "Да." it means you do not know the person. But in English, if I ask you, "Don't you know him?" your "Yes" answer would mean you do know the person. Am I right? In Russian one can say "Да, я его не знаю," but in English one cannot say, "Yes, I don't know him," one has to say, "No, I don't know him." This means sometimes Russian 'да' is translated to English as 'yes', but sometimes, when it is the confirmation of a negation, as 'no.'
Besides, Russian 'да' has several meanings. As a particle, it is 'yes' (or 'no'). It can be a question paricle, meaning 'right?'
"Ключ в столе, да?" - "The key is in the table, right?"
Also, it can mean 'by the way'
"Да, ещё одна новость." — "By the way / Oh yes, (there's) another piece of news."
It can mean "really?, indeed?"
"Вы знаете, он женился? - Да? А я и не знал." — "You know he has got married? - Has he? [Really / Indeed?] I didn't know."
It can be used for emotional emphasis - "but, oh but; why; well"
"Да не может быть!" — "But it can't be true!"
There are many other uses of 'да', but the phrase which is the scope of our question, "да нет", uses this last meaning of 'да', so it can be translated as "well, no" or "but no", or as "well, yes" or "but yes", if the question, to which it is the answer, contains a negation.
It means "No". There is also phrase "Да нет, наверное". That means "I guess no". But this phrase is used in only speacial situations. For example, if one person suggests another to go to the shop with him, the first person is not sure if he wants to go or not. But if he finally tells "Да нет", he means that he won't go. And almost always "Да нет" is continued with "Не" and a verb like "Да нет, не хочу".
It means "no". Particle "да", besides its main affirmative meaning, has many others. In this case, "да" is an emphatic particle, similar to "but" or "nay".
да has emphasizing function in this context. Compare:
Да пошёл ты! Да не надо мне здесь заливать! Да как сказать... Да ну его к чёрту! Да не может быть! Да как ты посмел?! Да на хрена он тебе сдался? Да что с тобой такое происходит в последнее время? Ходишь, как сам не свой. Да много ли мне надо?
In all these cases you can throw out
да, because it is used to increase the importance of what you are saying.
There are a few nuances where
да нет is appropriate (like others have mentioned above):
Да нет, всё как раз наоборот- Quite the opposite
Ты уверен, что сможешь это сделать? - Да нет. Не очень то.- Well, no
I guess "yes" and "no" in Russian and English are quite similar. It depends, however, on what deepness of language one wants to master. If someone wants to ask "Do you want coffee?" and one answers "да" for yes or "нет" for no, there is no difference. However, in Russian "да" in some cases acts as a conjunction meaning "and", e.g. "Иван-да-Марья" (literally "Ivan and Mary") is a name of a plant. Nowadays, "да" is used as a conjunction only in a small number of cases, mainly in expressions like "да нет" (a weaker or less-sure "no") or "да нет, наверное" (a even weaker form, where the person is not sure whether he agrees or disagrees, but slightly more disagrees) and in proverbs like "мал да удал" (small but clever).
The answer "да" to "Ты его не знаешь?" is not very clear for Russians too, but is grammatically and stylistically possible. Some people will ask '"да" what?' to know for sure what one means - "yes, you know him" or "no, I don't know him"?
As far as the peculiarities of colloquiallisms in Russian are concerned as well as, quite typically so, in English or other languages, more often than not they do not always appear to be going along the lines of logic or at least are likely to be viewed as such, pretty much confusing, as it were, by a non-native speaker. In the aforementioned phrase the "да" ingredient is used, in a nutshell, to express an emphatic "no" being used as a means to put an additional stress to the negative response rather than add to some cognitive ambiguity which one can possibly overcome with practice and experience. What's more, when attempting to deconstruct a spoken language, there's no way to treat any particle of it as redundant, since every single speck of it comes into existence in the course of natural process. I wonder if we can consider this very instance an interjection. To illustrate this with an example, here's a quote from L.Tolstoy's Kreutzer Sonata: — Ах, что вы! Да нет. Нет, позвольте, — в один голос заговорили мы все трое. Даже приказчик издал какой-то неодобрительный звук. Another example shows that it can serve a certain emotionally charged purpose, somewhat similar to "хотел, да не успел!". Sometimes the exclamation mark may read quite apt for that matter.
Just surplus info.
‘Genuine’ Russian ‘yes’ spells and is pronounced
да in your question, which is many times described in previous answers, in oral speech there are variants of this word which hardly can be heard (interpreted by ear) as ‘yes’-
да pronunciational variant. It can be pronounced with a final vowel varying around and resembling something like ы/а/schwa/and-their-shortened-varaints. (A form “
ды нет” can be found on the Internet.) Some more info is in Andrey Chernyakhovskiy’s comment below.
The phrase in question is really oral and that Russian
да нет does not tend to sound like English
*yes no or
"Да" in this case dosn't mean "Yes!": it's just an exclamation, like here https://en.wiktionary.org/wiki/да#Conjunction_5
So "Да нет" means "No".