Correction: "Once, I saw a youtube video that showed two women singing. I also read a few of the comments. In one comment someone said, 'You guys have amazing taste'. Why use 'guys'? Isn't a 'guy' a 'man'?" As the other members have said, "guys" can apply to several females, even though it traditionally applies to males. If the commenter had said "you girls...", it could be perfectly acceptable, but it could also have been interpreted as belittling to the women. So, "guys" is a safe though slangy option.

Thank you 'guys'! You answer immediately,so i am happy! I need study hard that English conversation after an absence of 20years.

I agree with the other answers :) Also, the title should read "I have a question for English speakers"

Guys is acceptable as an interchangeable term for "people". You could use it for a group of men, a number of men and women or strictly women.

You guys = people, both girls and boys.