Do Gregorian calendar, AD, Gregorian calendar and new calendar have exactly the same meaning?

It's different. Gregorian calendar is a calendar used by most countries in the world today, and its name is "Gregorian calendar", which is a kind of Gregorian calendar. "AD" is a mark added before the year in which the Gregorian calendar is used, such as AD 20 19 (these two words are omitted in most cases). Gregorian calendar is a calendar that determines the average number of days in a year according to the period of revolution of the sun. The solar calendars used in history and still in use today include julian calendar, Tian Li calendar of Taiping Heavenly Kingdom, Gregorian calendar (that is, the Gregorian calendar used now), Islamic Gregorian calendar, and Yi Gregorian calendar (October calendar). , not specifically referring to the Gregorian calendar. China began to use the Gregorian calendar in the Republic of China. At that time, some people called it "new calendar" for some reason, but now there are not many such words.