What attribute must be applied to a field in an index definition to ensure it is included in search results?

To ensure that a field is included in search results when defining an index in Azure Cognitive Search, it must be marked as "retrievable." This attribute indicates that the search service can return the field's content in search responses. When a field is set as retrievable, it allows the results to include the actual values stored in that field, making it an essential aspect of index configuration for effective searching and data retrieval.

The other attributes – searchable, filterable, and facetable – serve different purposes and do not directly determine whether the field's content will be included in the search results. Searchable fields are those that can be queried against text and support full-text search capabilities. Filterable fields allow queries to filter search results based on their values, while facetable fields enable the aggregation and categorization of results based on specific values. However, these attributes do not govern the retrieval of the field data itself, which is specifically managed by the retrievable attribute.