Dynamically Created Runtime Fields
The video contains a demonstration of the creation of an index template that defines that unknown fields will be created as runtime fields. Documents are then indexed into an index that inherits from that template, and because these documents contain fields that are not defined in the template, the fields are automatically created as runtime fields (i.e. these fields are usable for search and aggregation, but are not indexed). Runtime field is the name given to the implementation of schema on read in Elasticsearch.
For this video, you can use the following example runtime field API calls: https://github.com/giladgal/Examples-for-Elasticsearch-runtime-fields-API-calls/blob/main/Dynamically%20created%20runtime%20fields