@aowens-jmt Thank you for your question. Semantic search is a collection of query-related features that support a higher-quality, more natural query experience. Features include semantic reranking of search results, as well as captions and answers generation with semantic highlighting. You can find more details in the following link: https://aka.ms/semanticgetstarted.
Though we currently don't have a GA release date for semantic search, the capability is currently in public preview and we look forward to feedback from customers regarding their usage of semantic search features during the preview release. Please signup for the preview release at http://aka.ms/semanticpreview.