Just in case you are wondering...Thanks Wikipedia!

Girlfriend is a term that can refer to either a female partner in a non-marital romantic relationship or a female non-intimate friend.
The term is most commonly used to describe any female person who is in a romantic relationship with another person.
Partners in a non-marital relationship are also sometimes described instead as a significant other, partner or life partner especially if the two partners are living together. At times, since "girlfriend" and "partner" mean different things to different people, the distinctions between the terms are subjective, and which term is used in a relationship will ultimately be determined by personal preference.
When used by a girl or woman about another female in a non-sexual, non-romantic context, the two-word form "girl friend" is sometimes used to avoid confusion with the sexual or romantic meaning. "Girlfriend" is usually used in terms of very close friends and usually has no sexual connotation in that sense of its usage, unless it is in the case of lesbian, bisexual and pansexual women. The term also has currency in LGBT communities and can refer to people of any gender or sexuality.
Though nuanced, there is a significant difference between "girlfriend" and "boyfriend", and "girl friend" and "boy friend". In a strictly grammatical sense, a "girlfriend" or "boyfriend" is an individual of significance with whom one shares a relationship. A "girl friend" or "boy friend", however, is simply a friend identified on the basis of gender. The transition between the two is a significant aspect of adolescent development.
This term when used between men and women does not necessarily imply a sexual relationship, but is often used to refer to a woman who is dating a man she was not engaged to, without implying that she is having sex with him. . It is essentially equivalent to a prior term used, "sweetheart" which is also a term of endearment
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