Base, 360 (360 S, 360 E), One (One S, One X), Series (Series S and Series X)
Calling it the "S Series" or "X Series" would make sense, but "Series" as the base name of the product line is just...I mean, what were they thinking? It makes absolutely zero sense.
Meanwhile Sony's over here with PS1, PS2, PS3, PS4, PS5, and all the sub-versions make perfect sense (base, slim, pro, etc).
And Series X
And Xbox One S
And the Xbox Series S!
Huge if true
still waiting on the Xbox SX and then the enhanced Xbox SEX