There is a new filter in Community under Search Posts or under Filters for a specific channel: Keyword Sets 

This filter is only available for Community Managers, not Moderators or Owners of a channel.

In the filter menu, choose a keyword set.  The only posts displayed are those within that channel that contain one or more keywords in the set. 

The keyword filter can be combined with other filters such as date, users, and status.

Figure. Various filters available to Community Managers

Who can use the keyword filter in Community? 

The keyword filter is available to Community Managers, but not to channel owners or moderators.