Elasticsearch (and OpenSearch, the AWS-supported fork) is the dominant search and log-analytics engine for most workloads that need full-text search, log aggregation, or near-real-time analytics. The underlying Lucene engine has been the standard for inverted-index search since the early 2000s; Elasticsearch wraps it in a JSON HTTP API, distributed clustering, and the query DSL most engineers eventually learn.
Most courses cover the same cluster: index design and mapping, the Query DSL (must / should / filter / boost), aggregations for analytics, the ELK stack for log pipelines (Elasticsearch + Logstash + Kibana), and the operational concerns — sharding strategy, replication, hot/warm tiers, snapshot backup.