とは

See also: とば

Japanese

とは • (to wa)

indicates that a word or a phrase is to be defined or explained
素(そ)数(すう)とは何(なに)かを学(まな)んだ。
Sosū to wa nani ka o mananda.
I learnt what [the meaning of] a prime number was.

「原(げん)子(し)力(りょく)」とは？
“Genshiryoku” to wa?
What is [the meaning of] "nuclear power"?
(more emphatic) synonym of と (to, “with”)
あいつとはもう関(かん)係(けい)ない。
Aitsu to wa mō kankei nai.
I have nothing to do with them anymore.

過(か)去(こ)とは違(ちが)う自(じ)分(ぶん)
kako to wa chigau jibun
a self who is different from the [self of the] past
short for とは思わなかった (to wa omowanakatta, “did not think that ...”)
まさか自(じ)殺(さつ)するとは……
Masaka jisatsu suru to wa……
I never would have thought that he/she would kill himself/herself...

This particle is often used, for example, in encyclopedias to define entries.
When used alone with a word it denotes the meaning of "this word is defined as?" and may be translated as "about" or "What is".