I've being using Oracle for about 10 years, I never realized there is something called Materialized Views until I chat with my supervisor today.
So, what is Materialized Views?
From the help center: A materialized view is a database object that contains the results of a query. The FROM clause of the query can name tables, views, and other materialized views. Collectively these objects are called master tables (a replication term) or detail tables (a data warehousing term). This reference uses "master tables" for consistency. The databases containing the master tables are called the master databases.
In my understanding, it's a just a snapshot at the time people run the query statement.
I also noticed other item called Materialized View Logs. What's that?
From the help center : A materialized view log is a table associated with the master table of a materialized view. When DML changes are made to master table data, Oracle Database stores rows describing those changes in the materialized view log and then uses the materialized view log to refresh materialized views based on the master table. This process is called incremental or fast refresh. Without a materialized view log, Oracle Database must reexecute the materialized view query to refresh the materialized view. This process is called a complete refresh. Usually, a fast refresh takes less time than a complete refresh.
My understanding: a tool used to help synchronize the materialized views with the tables.