I like this question asking "What is a noun-modifying clause?", but I cannot decide (probably due to my lack of knowledge of linguistics) if this is a simple definition question, or a question that should be moved to the linguistics SE.
It has the potential to be moved, because what a noun modifying clause is is something that would be present across languages.
It could stay right here because it's asking for a definition of an English phrase.
Should it be here or there?
As the OP is talking of an example given him when studying Japanese, and the OP is asking for a term used for a specific clause, I would say the question suits better the site for linguistics. The fact he is talking about an example given when studying Japanese (a language completely different from English) makes me think the concept is not specific for English, and then it is not on-topic for EL&U.
To say it all, as the OP doesn't say exactly which was the example he was given in that Japanese study guide, the question is not completely clear.
