Zion is a fun little word, because it’s got a big ‘ole history of being confusing.
The earliest record we have of the word is 2 Samuel 5:7:
“7 Nevertheless, David captured the fortress of Zion—which is the City of David.”
So, the fortress of Zion was a stronghold of the Jebusites (a people who controlled the city of Jebus, more famously known as Jerusalem). And so, the whole mountain/hill that the fortress was on started to be called Mount Zion (also associated with the “Ophel”, but that’s a word for another day).
What does the word “Zion” mean? No clue!
Alright, well I have some clue. Pretty much, the current best guess seems to be that the word Zion comes from Hebrew ṣiyyôn, which means “castle” or “fortress”. This would make it literally be “the fortress of fortress” or “Mount Fortress”. It seems like a logical enough explanation, especially since plenty of languages name places like that (think of the Sahara Desert, where “Sahara” is just the Arabic word for desert). However, there are plenty of other guesses, and nobody really knows for sure where the word “Zion” comes from.
So, we’ve got this mountain that had a fortress called Zion, so that mountain is called Mount Zion. Is that the end of it? No, of course not!
There was another mountain, located just a couple thousand feet away, which was called Mount Moriah. This is the same mountain where Abraham prepared to sacrifice Isaac, and where Solomon built the first temple.
After Solomon built the temple on Mount Moriah, it started to be called “the Temple Mount”. However, for whatever reason, the term “Zion” also started to refer to the Temple Mount/Mount Moriah.
So, we’ve now got two mountains being called “Mount Zion”, one because there had been a fortress called Zion on it, and the other because of some sort of symbolic reason.
Then, about a thousand years later, just after the time of Jesus, the Jewish historian Josephus was writing his books. And, by that time Jerusalem had grown a whole lot bigger. Thanks to this growth, Josephus mistakenly started calling a bigger mountain near the center of Jerusalem “Mount Zion”. And guess what? The name stuck.
So, now we’ve got three mountains called “Mount Zion”.
And, in addition to all of that, the term “Zion” started to refer symbolically to: Jerusalem, the entire land of Israel, the spiritual Kingdom of God, the people of God, and the coming New Jerusalem.
Alright, that was a confusing word to write about, but that’s the gist of it. Zion can mean a lot of different things.