Is there one? Many people use "girl" as though it is, but when you consider that "boy" is really the male equivalent of "girl," the logic behind that really falls apart. I know this doesn't bug everyone, and the feminist community seems to be split on whether or not it is appropriate to refer to a woman over 18 as a "girl," but language, and how it intersects with gender, is one thing I'm particularly obsessed with. Language is the the first way that we humans tend to communicate with other people, and it shapes the ways in which we interact with others. Using "man" or other male pronouns, for example, as a default rather than gender-neutral language (humankind rather than mankind) leads easily into the wider men-as-default, women-as-other assumption we're all socialized with, and artificially influences power dynamics between individual men and women, among other things.
What we call the males of the species varies more than what we call females. Males have boy, guy*, and man. Females have girl and woman. Boy and girl mean the same thing: child**. Man and woman mean the same thing: adult. Guy typically means: young adult male. Since we have a common word to differentiate the area between childhood and full maturity for males, why don't we have one for females? There was gal, but that feels old-fashioned and outdated for everyday use. Chicks was problematic for other reasons, and fell out of common usage a while ago in mainstream culture. Most people who use "girl" for adult women say that they prefer it to describe 20- and 30-something women, because "woman" sounds too mature, and the image they see in their mind when they hear the word is a matronly, de-sexualized figure, and that's not the way they picture the person they're describing. But why use girl, which indicates a child, to describe a woman who's clearly no longer a child, when we rarely use boy to describe a man who's clearly no longer a child? It's infantilizing, and can get really creepy when you consider that, often, men who are referring to women they're sexually attracted to as girls are describing, literally, children. It's not that I think this indicates some kind of latent pedophilia among men who use "girl"; not at all. Calling adult women "girls" is definitely not a male thing. The inappropriate use of the term transcends gender. It's that women exist in this continuum of "sexy" and "mother" ("mother" being, by definition in our culture, asexual), with nothing in between. Sometimes you'll hear "young women," like a hasty clarification that the speaker doesn't mean old lady, but "young man" is another of those terms that sounds very old-fashioned that I never hear from people in my generation. There's nothing in-between, nothing neutral enough to allow for a broader understanding of females. That's my problem with "girls." I still use it on occasion (although it's usually followed with a *cough* "women"), but I struggle to find an alternative that is more equivalent to the highly useful "guy."
So what do we call adult females who are the same types of people who, if they were males, we would call "guys"? Is there something you say to refer to these women, which is considered an equivalent to "guys" where you live, or among your social circles? Because in mine, there isn't a word. Chicks isn't something anyone says unironically anymore, and even though we're all nearing 30 or just passing it, we all show clear discomfort when we force ourselves to say "women," while we consciously avoid "girls" for political or fresh age-related reasons, as we realize that we're all getting a little to old to be calling ourselves and our female peers girls.
*I realize that "guys" isn't a universally-used term for males somewhere between boy- and manhood, and is somewhat generational in its use, but there's usually an equivalent used for the term. Also, "guys" is often used to describe a gender-mixed group, which is also pretty split in terms of acceptability in different camps, because of its throwback to male-as-default language.
**My niece, who is three and a half, just told me a story in which she described an interaction with grown-ups, and she referred to them as "big kids, like you, and my mom!" So, maybe to some children, everyone's just a "kid." That's all right with me... so long as it's a toddler saying it.