Difference between the multilevel indexing and secondary indexing in dbms

Question

what is the exact difference between the multilevel indexing and secondary indexing in dbms as both appears same but classified different?

Answer 1

Secondary Index:

The secondary Index in DBMS can be generated by a field which has a unique value for each record, and it should be a candidate key. It is also known as a non-clustering index.

Multilevel Index:

Multilevel Indexing in Database is created when a primary index does not fit in memory. In this type of indexing method, you can reduce the number of disk accesses to short any record and kept on a disk as a sequential file and create a sparse base on that file.