とは

X means…
Word/Clause + とは

Meaning

とは is used to mark the thing being defined.
It essentially makes the word or clause before it into a noun via quoting と
It is essentially: 「A」は…

Frequently used with なんですか？and どういう意味ですか?
In informal situations, you may end the sentence with とは and omit 何ですか etc.

とは is an abbreviation of というのは.


This is so easy I am considering moving it to N3 or N4. Let me know in the comments what you think.

Applications

Common applications of とは are:

• To define a word
• To ask for the definition of a word, such as when googling something
• To ask for clarification or more detail on a statement
• Sometimes expresses discontent with the clarification usage

Examples

• 虚栄心とは？
  What is 虚栄心? (きょえいしん)
  
  
• 虚栄心とは、「自分を大きく見せようと見栄を張りたがる心」を意味します. (Source)
  虚栄心 (vanity) means  “The desire to present yourself as important and show off” 
  
  
• 「彼を片付けます」とはどういう意味ですか
  What does “I’ll clean him up” mean? (Fire him? Kill him? Yell at him?)
  
  
• 寝坊したとはどういうことだ？
  What do you mean you slept in? (It can also be used like this)
  
  
• マクドというのはマクドナルドの省略だ。
  (The thing called) Makudo is an abbreviation of McDonalds.