, occasionally seen in its kanji form 所謂（いわゆる）
, is a word that is used before nouns to indicate that something is ‘what is called (A)’, ‘the so-called (A)’, or ‘generally known as (A)’.
is a combination of いわ, a modern variant of いは, the indeterminate form of 言（い）う ‘to say’, and ゆる, which is the classical literary equivalent of the auxiliary verb れる, the displacement verb indicator in its attributive form. In this way, the literal meaning of ‘what is said to be (A)’ is carried over into the English translations.
Hamburgers and French fries are so-called junk food.
That is what is called a conspiracy theory, right?
This is what is called a loanword.
Fun-fact - The kanji for 謂（いい） means ‘oral tradition’, and highlights the way that something is referred to over the course of different time periods, or in different places.