Is there a word that is the feminine equivalent of guy? I thought of gal, but I think it is used for a girl, or a young woman. I am looking for a word that can be used to generally mean woman, and similar to guy.
According to the writers of this musical, it’s gal. In more recent times, however, guy seems to have become unisex.
In some cases "gal" can be used, and in some cases "girl" can be used. (for example "Girls night out" is more or less equivalent to "guys night out".) But although "girl" is sometimes used to refer to women of any age, it at least suggests a child or a young woman, and many women now consider it a mild put-down when used of an adult women, implying that women are never really mature. Once it was common to refer to a female workforce as "the office girls", but that would be taken as quite negative by many now.
There really isn't a female equivalent for "guy" in many usages. Some people use "guys" to mean "people", but I think that sounds odd, and depending on the context, perhaps wrong. There are many slang terms for "woman" but most of them have similar problems to "girl" or worse ones. It very much depends on the specific audience. "Lady" or "ladies" almost always works, but is a bit more formal than "Guy" or "Guys".
Guys seems to have a kind of casual almost affectionate ring that evokes a specifically male personna. The unisex usage seems a bit contrived, tag-along. Guy probably arose among men from sustained, all-male work, military, or school experience. Not having had many of those kinds of experiences women have evolved no generally informal terms for themselves. Maybe that will change.