Each Elasticsearch Shard is a Lucene Index

Elastic Stack Elasticsearch
1

Lucene%20Index
Lucene Index.PNG812×164 14.7 KB

I am not understanding the line "Each Elasticsearch Shard is a Lucene Index"

2

Elasticsearch uses Lucene behind the scene.
Elasticsearch splits indices into shards.
Each shard is a complete index engine powered by Lucene.