I owned an XBox One something. I believed "Series X" was short-hand for "Xbox One X", as I believed that there were maybe other kinds of "Xbox X". I even bought a game that didn't run on my console because it was for a "series" something, which was not actually what I had. "Series" is often used as an english word to identify a product line. Like "Is that the 'premium' series?"

Sometimes I joke about how confusing the xbox names are. I probably couldn't come up with a more confusing set of names if I tried.