Chunk of a
sentence, as opposed to a whole one. Sometimes just a
noun phrase. Also can be a
predicate with no
subject. Or a
sentence no verb. Very abrupt.
Not the same as
nonsense, as meaning can be had from
context.
Good grammar in Japanese — bad grammar in English. Common in casual speech, though. Also at the beginning of definitions and E2 writeups. Sometimes, all the way through.