Let's start with (3) "incomprehensible". This is a statement about something not being understandable. "comprehensible" means that it can be understood (分かりやすい). "incomprehensible" means it cannot be understood (理解できない?). (2) "mumbo jumbo" suggests that the content is not just hard to understand; it's nonsensical (ちんぷんかんぷん). It is a negative judgment about the content. (1) "over someone's head" means that it is too difficult for that person to understand. Now, we are not talking about the fact that something is hard for everybody to understand. We're saying that this person ("someone") is not able to understand it. This can be an insult that suggests the person is stupid e.g. "basic algebra is way over his head" Alternatively, it could also just say that the material is difficult e.g. "quantum mechanics is way over my head". Sorry, I don't know how to say "over one's head" in Japanese. There may not be a comparable idiom in Japanese. If you can think of a way to say it, please tell me so I can learn.

One more attempt to explain "mumbo jumbo". First, here's a link to the Merriam-Webster Online Dictionary entry: http://www.merriam-webster.com/dictionary/mumbo%20jumbo Next, a couple of examples: We were confused by all the legal mumbo jumbo. [We're not just confused by the legal text; we're saying that it is unnecessarily incomprehensible.] His explanation was just a lot of mumbo jumbo. [His explanation is not just difficult to understand; we believe it would make no sense even if we could understand it.] It may be interesting to know the origin of MUMBO JUMBO: Mumbo Jumbo was a masked figure among Mandingo peoples of western Africa So... you have to imagine European explorers going to western Africa and finding this inexplicable masked figure that is a central component of a pagan tribal religion. Their negative and contemptuous attitude is underneath the modern-day use of the phrase "mumbo jumbo". Definitions of "mumbo jumbo" (1) an object of superstitious homage and fear (2) a : a complicated often ritualistic observance with elaborate trappings b : complicated activity or language usually intended to obscure and confuse (3) unnecessarily involved and incomprehensible language : gibberish (4) language, behavior, or beliefs based on superstition

I like using this phrase "mumbo jumbo" when it is very difficult for me to fully understand what is being said, > No... "mumbo jumbo" means that you think no one can understand what is being said. You can soften it a little by saying "to me, it seems like mumbo jumbo" but the implication is still a negative judgment. or my other favorite word "incomprehensible" comes to my mind. I assume that the both words describe an extreme lack of understanding. I may not be correct though. > Once again, "incomprehensible" suggests that no one can understand it unless you say "it's incomprehensible to me" Today, I just learned this phrase "It's way above someone's head.". To me, these three sound like the same thing. so.. > No... see my other answer that explains the meanings of each of the three Q2) My second question is that how does native speakers use this phrase "It's way above someone's head." in everyday conversation? > Explained in my other answer.

Ai wrote 'I like using this phrase "mumbo jumbo" when it is very difficult for me to fully understand what is being said, or my other favorite word "incomprehensible" comes to my mind." Actually, the best way to say that " it is very difficult for me to fully understand what is being said" is to say "It's all Greek to me."