What does the word ZION mean in simple terms?

I'm assuming you're referring to the Biblical term…?

Zion is simply another term for the land of Israel (including Jerusalem). It is symbolic of the "Promised Land" — the land which God promised to give His children and in which He dwells.

Zion can (and does often) also refer to the hill in Jerusalem on which the Temple was built — "Mount Zion" — or even the Jewish people as a whole.

Zion (Hebrew: צִיּוֹן, tziyyon; Tiberian vocalization: tsiyyôn; transliterated Zion or Sion) is a term that most often designates the Land of Israel and its capital, Jerusalem. The word is found in texts dating back almost three millennia. It commonly referred to a specific mountain near Jerusalem (Mount Zion), on which stood a Jebusite fortress of the same name that was conquered by David and was named the City of David.

The term Zion came to designate the area of Jerusalem where the fortress stood, and later became a metonym for Solomon's Temple in Jerusalem, the city of Jerusalem and the entire Promised Land to come, in which, according to the Hebrew Bible, God dwells among his chosen people.