When combined, 工资 (gōngzī) means “work money,” which is the perfect way to describe a salary or wage. Adding 发 (fā) in front turns it into the action: 发 (to issue) + 工资 (wages) = to pay a salary.
The concept of payday is universal, but “发工资” in China carries a distinctly social and communal flavor.
“发工资” is a high-frequency term used in various everyday situations.
The connotation is almost always positive and exciting. The only time it's negative is when it's used in a negative sentence, such as when a company is late with payments.