星期五，又称礼拜五或周五。指的是一周中星期四之后、星期六之前的那一天。星期五的拉丁语名字是dies Veneris，意思是维纳斯日或金星日；法语是vendredi，来源于拉丁语；英语是Friday，来源于日尔曼的爱与美的女神，大神奥丁的妻子弗丽嘉；俄语是пятница，意思是“第五天”。

在古代中国、台湾日治时期、现在的日韩朝，一星期以「七曜」来分别命名，星期五叫金曜（yào）日（韩语：금요일）。在中国大陆民间口语称礼拜五，在台语中简称拜五。

根据基督教的传统，星期五是耶稣受难的日子（受难节），所以部分基督徒认为星期五是不祥的日子，一般教会不会选择在星期五进行礼拜。这一天亦是穆斯林举行聚礼的日子。

Friday is the day after Thursday and precedes Saturday. In countries adopting Monday-first conventions as recommended by the international standard ISO 8601, it is the fifth day of the week. It is the sixth day in countries that adopt a Sunday-first convention. In other countries (see workweek and weekend), Friday is the first day of the week-end, with Saturday the second. In Afghanistan and Iran, Friday is the last day of the week-end, with Saturday as the first day of the working week. Bahrain, the United Arab Emirates (U.A.E.) and Kuwait also followed this convention until they changed to a Friday–Saturday week-end, on September first, 2006 in Bahrain and the U.A.E., and a year later in Kuwait. In Iran, Friday is the only week-end day. In Saudi Arabia and the Maldives, there are two week-ends where Friday is the first week-end of the week while Saturday is the second week-end.