A better question would have been 'what is semantic search' as you need to understand that in order to be able to focus your SEO efforts to get the best out of it. Read the Wikipedia entry on semantic search for a quick overview.
SEO means search engine optimization. seo is a stradgy by which you can get keywords ranking search engine results pages. there are two types of seo on page seo and off page seo. now seo is very popular to get organic results which is very helpful to get business.
SEO is the provide out website increasing by organic and naturla traffic. and talking about Sementic SEO so that point of view this is the new web marketing process. and that unnecessary link is delete and purely effected links visible in search engine.
According to Moz "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."