There is a filter in Community called Keyword Alerts. 

It can be found for any given channel, or you can filter the entire Community by selecting "Search Posts" and then applying the filter.

In the filter menu, choose a keyword set.  The only posts displayed are those 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 1. 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.