Girlfriend
The term girlfriend is usually used in one of two forms, both implying intimate friendship.
When describing a girl or woman as "girlfriend" of a woman, it is usually used in terms of very close friends. It usually has no sexual connotation in that sense of its usage (although it can in the case of lesbians or bisexuals).
When describing a girl or woman as "girlfriend" of a man, it is almost always used to refer to a woman that is involved in a romantic relationship or sexual relationship with that (or a) particular man. The equivalent male term is boyfriend.
Change in usage
Until the last decades of the twentieth century, this term when used between men and women generally did not necessarily imply a sexual relationship, but was used to refer to a woman who was dating a man she was not engaged to, without implying that she was having sex with him. It is still used in this sense when talking about young teenagers (or even pre-teens). With the changes in sexual mores in effect now, the term dating when used to indicate that an adult man and woman have gone out together on a date, now strongly implies sexual activity between them.
It is essentially equivalent to a prior term used, sweetheart.
See also
