という

1. 1Names or identifies something: "a N called X".Ex. 1
2. 2Reports what someone said, with the quotative と plus the verb 言う: "say that ~".Ex. 2
3. 3Links a clause to a noun that states its content: "the news/story that ~".Ex. 3

It is used in both speech and writing to introduce names that may be unfamiliar to the listener and to report what someone said. In the naming and content senses, いう is normally written in hiragana, while the verb meaning "say" is usually written 言う. In conversation, って takes the place of the quotative と (〜って言う) or of という itself (〜っていう, 〜って + 名詞).

• 1.
  ってN4って is the colloquial form of という or the quotation particle と, and can replace them for naming, quotation, content, and hearsay; it can also introduce a topic like というのは. In formal contexts use という and と instead, and for topics use は or というのは.
• 2.
  とN5Noun + と + noun means "and" and refers to two separate things, while in AというB, A is the name of B, so they refer to the same thing. When と appears alone after a sentence it means "as soon as...", and for quotation it is followed by verbs like 言う.
• 3.
  〜と言うN4〜と言う has the same quotation-of-speech meaning as という and the two are interchangeable, with 〜と言う usually written in kanji. When meaning "called..." or explaining content such as 話, it is usually written as という. It also has the form 〜と言われている, meaning "it is said that".
• 4.
  ということN4ということ is a fixed combination of という plus こと, functioning as a whole as the subject or object and meaning "the fact that...", often used with verbs like 知る and 聞く. という by itself cannot serve as a subject or object; it must attach to a concrete noun, or be used for quotation or sentence-final hearsay.
• 5.
  というのはN3という modifies nouns, or expresses "say" or "it is said that"; というのは raises a word or matter as a topic and is followed by a definition or explanation, and when used at the start of a sentence it can also add a reason for the previous sentence. The two cannot be interchanged.
• 6.
  ということだN3ということだ is used only at the end of a sentence: when expressing hearsay it is close in meaning to sentence-final という and the two are generally interchangeable. It can also express a conclusion meaning "in other words", but it cannot introduce a name or modify a noun.

って is the conversational form that replaces the quotative と (〜って言う) or という itself (〜っていう), と is the quotative particle alone, and 〜と言う is と plus the verb "say", i.e. the reported-speech use of this pattern. ということ turns a clause into a noun, というのは introduces a term to be defined or explained, and ということだ reports hearsay or states a conclusion.