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

というのは is a phrase that combines the case marking particle と, the う - Verb 言(い)う, and the nominalizing particle combination のは. Together, they are usually translated as 'the ~ known as ~ is ~', or 'the ~ called ~ is ~'. Sometimes, it can even simply be '~ means ~'. In essence, というのは is just a way to turn an entire phrase into a noun, before explaining that noun further. This explanation of (A) will either be to give a definition of it, or to give a reason for it.

To use というのは, attach it to the end of a phrase that you would like to indicate as being something that will be explained further '(A)', and then follow it with your definition/reason, '(B)'.

Caution

Unlike というのは, which is mainly used to strongly present facts, or highlight points of discussion, replacement of は with the adverbial particle も can be used either as a rebuttal or as an extension of the original statement. This is when someone wants to show that (B) has equal weight when compared to (A). It may also be used to give the reason or cause for (A).

Caution

というのは is sometimes used at the beginning of a new sentence, when the speaker wants to add extra information about what has already been said. In these situations, the translation is similar to 'what I mean to say is ~', or 'because of that, ~'.

Caution

というのは is regularly abbreviated as とは, or って. This can be a little bit hard to identify in casual speech, but the '(B) explains (A)' concept will still almost always apply, so should be identified that way.