所谓……就是……, 也就是说: defining and restating
【高81】【高125】固定格式、解说复句 / set structures
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
所谓 A，就是 B: “what is called A is B”. It is the pattern of definition in a lecture, thesis or talk: name the notion, then describe it (所谓方言，就是通行于某一地区的语言变体). After a subject, 所谓 attaches to the noun with 的 and often takes an ironic tint: 他所谓的好家庭 = “what he calls a good family”.
也就是说: “in other words, that is to say”. It restates the previous clause or draws its direct consequence: 这是我的决定，也就是说不关你的事. What follows must repeat or extend what precedes, never contradict it.
Both spell things out: compare 换句话说 (hsk5-g26), which stresses the rewording, and 即 “namely” (hsk6-g19), more literary. Register: careful speech and writing.
Examples
所谓知足，就是对已有的东西感到满意。
Suǒwèi zhīzú, jiù shì duì yǐ yǒu de dōngxi gǎndào mǎnyì.Contentment means being satisfied with what you already have.
所谓方言，就是通行于某一地区的语言变体。
Suǒwèi fāngyán, jiù shì tōngxíng yú mǒu yí dì qū de yǔyán biàntǐ.A dialect is a variety of a language used in a particular region.
房内没有一样值钱的东西，所谓家具就是这几把椅子。
Fáng nèi méiyǒu yí yàng zhíqián de dōngxi, suǒwèi jiājù jiù shì zhè jǐ bǎ yǐzi.There is nothing of value in the room; the so-called furniture is just these few chairs.
他所谓的好家庭就是住在一栋大房子里。
Tā suǒwèi de hǎo jiātíng jiù shì zhù zài yí dòng dà fángzi lǐ.His idea of a “good family” is simply living in a big house.
这是我的决定，也就是说不关你的事。
Zhè shì wǒ de juédìng, yě jiù shì shuō bù guān nǐ de shì.This is my decision, which means it is none of your business.
公司明年不再招人，也就是说，今年毕业的同学要另找出路了。
Gōngsī míngnián bú zài zhāo rén, yě jiù shì shuō, jīnnián bìyè de tóngxué yào lìng zhǎo chūlù le.The company will not hire next year, which means this year's graduates will have to look for another way out.
Common mistakes
✗ 他所谓好家庭就是大房子。 → ✓ 他所谓的好家庭就是大房子。 (after a subject, 所谓 attaches to the noun with 的).
✗ 我很忙，也就是说我很闲。 → ✓ 我很忙，也就是说没时间陪你。 (the second clause must restate or extend the first, not contradict it).