A search view is a saved search over one of the Elasticsearch indexes: the master index, which holds pages, posts, books and the other content, or the facets index, which holds products with their facets. The view decides what can be searched, filtered, sorted and highlighted, and which of those a request may change; a request can change only what the view allows.
A site’s own search page renders a view with no API call. This route is for an integration or a headless front end, which calls it from its server: members are refused.