Here is a Moz blog post that addresses this quite well:
...there is a concise definition of semantic search provided by Tamas Doszkocs of WebLib:
"Semantic search is a search or a question or an action that produces meaningful results, even when the retrieved items contain none of the query terms, or the search involves no query text at all."
...However, there's still not an agreed-upon term to describe the activities around achieving visibility in the semantic search results or optimizing for a semantic search engine.
I've heard everything from "entity-based SEO" to "entity SEO" to "Search Entity Optimization" as descriptors for optimizing around entity-based results. I'd personally lean towards "semantic search optimization" or "semantic SEO," but I can guarantee one thing: It doesn't matter what you call it at the end of the day. Adjusting to the semantic search landscape will be part of the SEO's job description going forward.
So "semantic search" is the new way that search engines are ranking pages for queies and "semantic SEO" is how to optimize sites for semantic search.