In the popular TV quiz show "Jeopardy!" , I always hear the contestants respond to the question by "What is…", many times in a certain or uncertain tone. (When the key word is a person, they say "Who is…")
Since I started to learn English as a little boy, I have learnt that "What is…" is a question to ask for particular information about something. For instance, "What is that?","What do you have?",etc. Also, "what" can be used to make a suggestion, like "What about…?", or to introduce a clause.
But I can't explain why those contestants use "What is…" that way. And the host, Alex, judges their "What is…" by "that's it" ,"correct","you are right" ,"yes"or "no".
Why don't they say "That is…" ,"What about…,"or "Is that…", which sounds more grammatically correct to me?
Since there are all native speakers in that TV program, I believe they say "what is…" for a reason and this expression must be correct. I do want to know what is the grammar while using "what is…" that way?