@MONTH(date-number) extracts the month, a value from 1 through 12, from date-number.
date-number is a value from 1 (January 1; 1900) through 2958525 (December 31; 9999).
You can use one of the other date @functions to supply the value for date-number.
@MONTH(@DATE(91;3;27)) = 3 because 3 is the month argument for @DATE(91;3;27).
@MONTH(20181) = 4 because the date number 20181 is the date 02-Apr-55.