In version 1.2 and later the Filter source is called the Last search.
When using the Source: Filter in Opening Explorer you are presented with only the moves and statistics from the filtered database games for the current position on the board. You can narrow the current filter down to only those games which have the current position in them simply by clicking the Show games button. Please see the Opening preparation section for details on how Opening Explorer can be used for top class opening preparation.
In the above example I searched for only games played by Garry Kasparov with the White pieces with players over 2600, in that way the Opening Explorer pane can give you the repertoire of a particular player in any position.
When you see [end] as a move this indicates one of the games ended at this point.