Hasan Rahhal gives a good introduction to ElasticSearch:
On the top level hits.total is the total number of the docs using an empty search query, and max_score is the maximum score a document can take in a specific query. In our case it’s one, since no query was specified.
In __shards.total_ the value is the number of Lucene indexes that Elasticsearch created for that index. The default number is always 5 unless we specify otherwise on index creation time. More details about shards are explained here.
ElasticSearch is designed to store things like logs and monitoring metrics, and the interface is JSON. This makes it very useful for certain tasks and infuriatingly difficult to do other things (like advanced aggregations). Still, in a medium-sized or larger environment, this is probably a technology you either are using today or want to use.