Feminine is the opposite of masculine. If it has anything to do with girls and women, it's considered feminine.
Anything feminine is associated with females. In American culture, that includes wearing pink, playing with dolls, sporting high heels, and getting weepy during sad movies. Many women find the traditional feminine roles to be sexist and limiting, while many men pick on each other for acting in a stereotypical feminine manner. But ideas about what is feminine are always changing: pants used to only be a masculine thing to wear, for example.