Semantic search is all about search with meaining. Versus the alternative of looking for literal keyword matches without understanding the meaning of the query.
The purpose of understanding the search query or intent of the question being asked is to provide more relevant answers. Without context, the result or search relevance could be different. However with context including location, time of day, season, intent, synonyms, and conceptual understanding you can better answer the question.
To understand search intent you must be able to decode the search terms and associate meaning. Using semantic search engines you can understand spelling errors, user location, user search history and different entities (people, places, things).
As an example, the words “cheapest” or “best” can be interpreted differently based on your needs and budget. If you were shopping in a store the salesperson would probably need more information to make a relevant suggestion.