"Guys" - technically, it means males, usually used to refer to young men. However, if someone uses "Hello guys!" or "Hi guys!" in a casual context, it's the same as saying "Hi everyone!". Just don't use it like that in a formal setting.

"Hello, friends." "Hello, colleagues." It's slightly informal. It's appropriate if everyone in the group is a person you are on a "first-name" basis with. It is acceptable in a business meeting if everyone at the meeting calls everyone else by their first name. In the 1950s "guy" meant "man" but my feeling is that in the U.S. today it is completely gender-neutral.

Hello Carlos, Thank you for answering my question.