When combined, `礼拜 (lǐbài)` means “worship” or a “weekly religious service” (specifically a Christian one). The days of the week are then numbered following the day of worship, which is `礼拜天` (Sunday). Therefore, `礼拜二` is the “second day” of this cycle, which corresponds to Tuesday.
The existence of the `礼拜 (lǐbài)` system for days of the week is a direct linguistic footprint of Western cultural and religious influence in China, primarily through Christian missionaries in the 19th century. Traditionally, China used a lunar calendar with complex systems like the 24 solar terms (`节气 jiéqì`) to mark time, but it did not have a seven-day week cycle. The concept of a seven-day week was introduced from the West. This led to the creation of three different systems: 1. 星期 (xīngqī): “Star Period.” The most common and secular system, based on the ancient concept of seven celestial bodies (Sun, Moon, and five visible planets). This is the standard in mainland China. 2. 周 (zhōu): “Cycle” or “Week.” The most concise and often used in formal or written contexts. `周二` is very common on schedules and in official documents. 3. 礼拜 (lǐbài): “Worship.” This system, rooted in the Judeo-Christian tradition of a Sabbath or day of worship, became popular and remains so, especially in Southern China and Taiwan where missionary activity was historically strong. Comparing this to Western culture, it's akin to the difference between calling the last day of the weekend “Sunday” (from “Sun's day”) versus calling it “the Lord's Day.” Both are understood, but the latter reveals a specific religious origin. In Chinese, however, these different systems are all in active, mainstream use, making it a unique linguistic feature.
`礼拜二` is widely used and understood throughout the Chinese-speaking world, but its frequency varies by region and context.