The combination “星期” (xīngqī) literally translates to “star period.” This term was adopted from the ancient Babylonian seven-day week, which was based on the seven classical celestial bodies (the Sun, the Moon, and five visible planets). Adding “六” (six) simply marks it as the sixth day of this cycle.
The concept of the modern seven-day week, and the term “星期” itself, is a relatively recent adoption in China, borrowed from the West for its practicality in international scheduling. In modern China, Saturday is the heart of the weekend, or “周末” (zhōumò). This wasn't always the case. Until the mid-1990s, China operated on a six-day workweek, with Saturday being a full or half workday. The transition to a five-day workweek, known as “双休” (shuāngxiū, “double break”), dramatically changed the cultural role of Saturday. It transformed from a day of winding down work to a full day of leisure, shopping, family gatherings, and social activities. Compared to the Western concept of Saturday, the activities are very similar. Malls are packed, restaurants are busy, and young people meet with friends. However, there's often a strong emphasis on either catching up on supplementary classes for students or spending time with extended family, reflecting the persistent importance of education and family in Chinese culture.
“星期六” is the standard, neutral term for Saturday used in virtually all contexts, from formal business emails and news reports to casual chats with friends.