Xmas is an abbreviation for Christmas that should not be used in business writing.
A yes/no question is one that can be answered with a yes or no response. These questions normally begin with an auxiliary or modal verb.
Example: Do you want to see it?
Example: Did you find it?
Example: Will they like it?
Zero article describes a situation where a noun is used without an article like the, a, or an.
Example: Money is power.
Example: We are studying French.