What is an explicit location of a query

An explicit location is when instead of searching for example for "Chinese Restaurant", you search for "Chinese Restaurant in New York City".

By default, the results provided by "Chinese Restaurants" will be based on where you are, assuming the search engine can determine your current position based on your GPS data for example, your IP address, or at least your ISP (if you are in let's say Los Angeles, it will show you results around Los Angeles). That's called "implicit location".