Evan, I think in the case of Winter Queen strain, they mean it's a group of plants which share similar characteristics of color, height or habit to the ORIGINAL named cultivar. It happens often in lilies. These are seed produced.
This would be as opposed to clone, which would be division produced, or test tube produced. .
So, I would say Winter Queen is the cultivar name, and it should be noted it's a strain and therefore variable.
I'm not sure about series. I would think series might contain strains. Series would be something like Bob said, that a company would produce. Like Northwest produces the Winter Jewels series, and Barry Glick produces the Sunshine series. But I would think these series could be made up of strains. Especially in the case of the Sunshine series. I'm pretty sure Barry produces all his from seed.
