In Elasticsearch, a query is a request for information from an Elasticsearch index. It is used to search for documents that match specific criteria or conditions.
There are several types of queries in Elasticsearch, including:
1. Full-text queries: These queries match documents based on the content of the text fields in the index. They can be used for simple keyword searches or more complex queries that use features like fuzzy matching, phrase matching, and proximity matching.
2. Term-level queries: These queries match documents based on exact or partial matches of specific terms or phrases in the index. They can be used to filter documents based on specific criteria, such as a date range or a category.
3. Compound queries: These queries combine multiple full-text or term-level queries into a single query. They can be used to construct more complex queries that combine different search criteria.
4. Joining queries: These queries are used to join documents in one index with documents in another index based on a common field. They can be used to construct complex queries that span multiple indexes.
Elasticsearch provides a powerful query DSL (Domain-Specific Language) that allows you to construct queries using a JSON-like syntax. You can also use the Elasticsearch Query DSL API or a number of client libraries to construct and execute queries programmatically.