Index fund classification:

First of all, fully replicated index funds. This kind of index fund generally replicates the index 100% and adopts a completely passive strategy. We can illustrate, for example, that if you are a student and you want to track the performance of another student who is particularly good at learning, assuming that you can track the performance of the first place in the class, there are two ways to achieve it. The first method is to ensure that every subject is close to or consistent with his grades, which is equivalent to complete plagiarism.

Second, enhanced index funds. Still the above example. In the second way, you may think that your advantage in some courses is not obvious than that of the first student, but you have other courses that are better than that student, or at least have similar advantages, so you can choose other courses instead of following a certain part of that student's courses to get similar results. This is equivalent to adding active investment strategy on the basis of passive investment, which is an enhanced index fund.