In Chinese numerology and superstition, the number four is often avoided because its pronunciation resembles the word for death.
In Mandarin, four is sì and death is sǐ; the tones differ, but the sound similarity is close enough to support the association. Comparable similarities occur in several other varieties of Chinese, though pronunciation and strength of the taboo vary by language and region.
This fear is known as tetraphobia. Buildings in some East Asian communities may omit fourth floors, room numbers, or telephone numbers containing four, much as some Western buildings omit the number 13. The practice is especially visible where cultural beliefs influence design and marketing.
The taboo is not an absolute rule. Many people use the number normally, and attitudes can differ by generation, location, and context. It is also distinct from the positive associations attached to other numbers, such as eight in Chinese culture. The superstition is based on phonetic resemblance, not on a mathematical property of four.