The supreme god of ancient Chinese religion, a name missionaries took for the Christian God; Protestants use it, Catholics say 天主. Everyday sayings use it too: 顾客就是上帝, 'the customer is God'.
Missionaries split over 上帝 versus 神 for 'God', so the 1919 Protestant Bible, the 和合本, came out in two editions, one with each word. To keep the pages identical, the 神 edition puts a blank space before the word.
usage
In Chinese, different religions use different terms: 上帝 (Christianity), 真主 (Allah in Islam), 佛 (Buddha). 天 (heaven) is also used as a general concept of a higher power.