SEO, otherwise known as Search Engine Optimization is an effective way to work on improving your online visibility on the SERP. It revolves around traditional searches (regular search) where a user types a particular keyword, long-tail keywords, or fragmented phrase in the search box to find the answer to his question/query. It uses keyword research (long-tail keywords), content creation, and page optimization.
Voice Search Optimization is a more specified kind of SEO. It is SEO for voice. The method user uses to search his query online makes about the difference between SEO and VSO. The strategies of voice search impact on SEO. For voice search queries, use natural sentences and questions in natural language. There is no need for keyword research, long-tailed keywords or, long-tail fragmented phrases.