The overview panel shows Health with one moniker of {good, warning, critical}.

These monikers have an exact meaning defined by a comment in the code as:

     // table health status:
     // good : all shards (primary and replicated) are started
     // warning : all primary shards are started && at least on replicated shard is not started
     // critical : at least one primary shard is not started

It would be nice to have a help hint on hover over the moniker in the UI displaying the definition.
and/or
add a note in the overview document, defining the monikers.