Are there any terms (preferably used in English, but Japanese is also ok) about whether a word is written in kanji or in kana?
I think this issue is precisely captured by the concept of jōyō kanji.
Dictionary entries will often look something like this (from Daijirin)
- す・る 【刷る・▼摺る】
- する 【▽為る】
- ▼摺 means that the kanji 摺 is not a jōyō kanji, and
- ▽為 means that the kanji 為 is a jōyō kanji, but not with the reading 為る【する】.
In particular, from this information you can deduce the following:
- 刷る "to print" is usually written with kanji
- する "to do" is usually written in kana
I think you should replace the concepts of "usually kanji" or "usually kana" by "is a jōyō kanji (or reading)" or "is not a jōyō kanji (or reading)".
As far as I know, kanji is used to separate words and ideas, since in Japanese they don't use spaces, it works as a way to separate ideas, also some of the kanjis have a "name usage" meaning that it has a specific sound for it when you want to use it to add or mention a persons name/last name.
I don't think there are general rules of where you can't write a kanji in kana, specially if you are a foreigner learning the language, although it will look weird to local japanese people.
No, I don't think we have any particular term for whether we wright in kanjis or kana. You can name it.
We just distinguish which characters to write in accordance with contexts.
It's just like English doesn't have exact terms for 消費期限/賞味期限, Which goes like this