said by Kearnstd:as far as I am concerned they are meaningless. 1 series is a small car, 3 series is a sports coupe, 5 series is a mid sized luxury sedan, 7 series is the land yacht that is in the same market as things like the Cadillac DTS.
But for people that care, 3-series is not very descriptive.
I have a 3-series.
CylonRed
has a 3-series.
But he'll tell you they are completely different cars. I have an E90, he has an E46 (and he probably thinks an E90 is not a proper 3-series).
You could convey the same info by model year, but then you'd have to know stuff like when the model changed. (The switch from E46 to E90 was for the 2005 model year). And really, the year isn't as relevant. A guy that's interested enough to want to buy a (used) E46 likely is not so much concerned with the exact year as much as he wants that particular model. Yeah, there are year-to-year differences, but they're overshadowed by the complete body-style change.
Me, I don't care (but then, I drive an E90) but I pick up stuff from the gearheads now and then.