$lexical in collections

$lexical is a reserved field in documents that stores a string. This string is indexed and used for the lexical search component of hybrid search. During a lexical search, this string is compared against a string of space-separated keywords or terms using keyword matching techniques.

Only collections that have lexical enabled support the $lexical field. For more information, see Create a collection.

In order to be included in a hybrid search, a document must have both the $lexical field and the $vector field populated.