The index option controls whether field values are indexed. It accepts true or false and defaults to true.

Indexing a field creates data structures that enable the field to be queried efficiently. Numeric types, date types, the boolean type, ip type, geo_point type and the keyword type can also be queried when they are not indexed but only have doc values enabled. Queries on these fields are slow as a full scan of the index has to be made. All other fields are not queryable.