What is yes?
yes is (adv) a word showing that you agree or accept etc., the opposite of ‘no’ They asked her if she wanted to come and she said ‘yes’. Anyone want more coffee? – Yes, please. You don’t like living in Lon- don? – Yes I do! Didn’t you work in Scot- land at one time? – Yes, I did. I need a clear answer – is it ‘yes’ or ‘no’? Synonym affirmative. Antonym no
source: Easier English, Student Dictionary Upper Intermediate Level