A magical girl series refers to a series that follows the story of a young girl (usually around adolescent to teen) who one day receives a power to transform into their alter-ego superpower to fight evil.
The transformation process is most basking themself to light while the outfit attaches to the girl themself. For some reason, the enemy does not attack until the girl is done transforming. Magical girls often wear sexy or revealing outfits and use a cutie-looking weapon as their choice.
In the Drillimation Universe, the Magical Girl Team Lucky Star is a magical girl anime and features lots of magical girls.