と言(い)うのは~ Known as ~ is, ~ Called ~ is, ~ Means ~, Because

The grammar point ことなの conveys a more plain, descriptive or explanatory tone, stating something as it is, or defining what something means. On the other hand, というのは provides a sense of context or reason to a situation or statement and is often used to introduce or explain a subject in a conversation. Additionally, it's also used for definitions or speaking metaphorically, hence it can sometimes overlap with the use of ことなの.

The phrase というのは can serve as an explanation or commentary, usually used to introduce a subject, define it, or give background information, while the phrase ということは is used to infer or deduce a conclusion from a previously stated or known fact. Therefore, というのは often provides the basis for discussion, and ということは is typically used to draw a conclusion or elucidate a matter based on that discussion. It's essential to recognize that ということは generally follows a cause-and-effect structure, while というのは often sets the stage for an explanation or description.

While both ということ and というのは are used in Japanese grammar to clarify, define or explain something, they have slightly different nuances and usages. ということ is used to express the concept or idea of what is stated, thus nominalizing clauses so they can be the subject or object of a sentence. On the other hand, というのは is used to provide explanations or definitions to a preceding sentence, often carrying a nuance similar to 'speaking of which' or 'the thing called.' The former is more general and adaptable, whereas the latter serves a more specific function of clarifying or elaborating on the mentioned topic.

Both という and というのは are used in Japanese to provide explanation or definition about a subject. However, while という can be used to introduce a topic or clarify what you're referring to (such as in 'The book known as...'), というのは takes it a step further and often provides a reason or deeper explanation and context (such as in 'The thing called... is because'). Therefore, というのは often carries a nuance of emphasizing or expanding upon the point being made.

The phrase "いわゆる" is used when referring to something that is commonly known or generally referred to by a specific term or explanation. It emphasizes that the term is widely recognized or understood by others. On the other hand, "というのは" is used to explain the meaning of something, clarify what you are referring to, or to give a reason for something. It is often used to introduce or define a specific term or concept that may not be universally known.