They are used to treat an object as an Array.
! Indexers are implemented using 'this' keyword.
! In Indexers the get and set get called with a variable which is the array parameter value.
! A property is identified by its name, an indexer by its signature.
! They can't be static.
! In indexers when we are overriding code in the derived class, we would like to call the original indexer in the base class first.