This is a new type of index introduced in sql server 2012. This is a non clustered index based on a column. This will increase the query performance when involving in a huge volume of data in the data warehouse face tables.
Usually the requested columns in a query will be returned after all the pages fetched in to memory. In this approach Whatever columns we include as column index, all of them are stored as columns within the index and data no longer stored by row. Only the requested column fetched in to memory. When we use the columnstore indexes it can reduce disk I/O and utilize memory more efficiently.