Yes, "guy" can be used informally to refer to both men and women in casual, conversational English. Over time, the word "guy," which traditionally referred specifically to males, has evolved in some contexts to become gender-neutral when used in the plural form, like "guys."
### When to Use "Guy" for a Girl:
1. **Plural form ("guys")**:
- It's very common to hear people refer to a mixed-gender group as "you guys," even if the group includes only women. For example, saying "Hey, you guys!" to a group of women is widely accepted in informal settings.
- Example: "Are you guys ready for the movie?" (said to a group of women or a mixed group).
2. **Singular form**:
- Using "guy" in the singular to refer to a specific woman is less common and might sound odd. If you say "She's a great guy," it can be confusing because people usually associate "guy" in the singular with males.
- Example: "She's a cool guy" could be jarring, but "They're great guys" when referring to women would sound normal.
### When it might not work:
- **Formal or professional settings**: The term "guy" is generally informal. So, in formal settings, it's better to use specific gendered terms (like "man" or "woman") or gender-neutral terms like "person" or "individual."
- **Cultural context**: Some people may still feel that using "guy" for women is inappropriate, depending on their personal or cultural background.
In summary, using "guy" for a girl is common in the plural form, but it’s best to avoid it in more formal or singular situations to avoid confusion.