Girls' day/night out means that a group of female friends have arranged to go out shopping or to a restaurant without any men.

Girls' Day might mean that girls have planned a time when the girls will go shopping together, with no men invited to go along -- only the girls. It might mean that a bar or event has set aside one night that only girls can attend. It is definitely a time that the girls will be together, and maybe the men are taking care of the children or doing the cooking while the girls are having fun. These girls are grown ladies, but they are calling themselves "the girls". They could say "Women's Night Out", and either way is fine.

If ou have one, you and your friends that are girls will do the things you want without talking to your boyfriends and husbands. They will not be there either.

girl´s day- a day dedicated to girls. :)