Filtered indexes are an excellent performance tuning feature found on SQL Server 2008 and later. Basically, by adding a WHERE clause to a CREATE INDEX statement, you can make the index smaller, more specific and faster.
Catalog views: Database objects
Catalog views are system views that expose most facets of the server and its databases in a tabular form. In this tutorial, we’ll take a closer look at database objects and how they’re represented in a database’s catalog views.