An English example would be, 'We have seen a lot of changes, which are good for business.' or a follow-up question in a casual conversation, '..Which is?'
I was wondering if they have an exact word or phrase for this, or do they have a similar concept?
Arigatou!
This type of noun-modifying clause is called relative clauses (関係節 or 連体修飾節 in Japanese). The Japanese language has the same concept, but the word order is drastically different. This answer is a quick starter, but this is a difficult topic which can take months to get used to, so I recommend reading your textbook.
(If you are already familiar with basic relative clauses and searching for the name of this special type of relative clause, please read this answer. Note that this is an advanced topic to a beginner.)
As you will soon realize as you begin to learn this concept, Japanese relative clauses must be placed before the modified thing. Therefore, Japanese has no direct equivalent of 'Which is...?' as a follow up question said at the beginning of a sentence. Instead, you can just say "つまり…?" ("That is...?") to ask for the conclusive or summary statement.
