parergon n. a secondary, derivative, unnecessary, or supplemental occupation, ornament, or (creative) work. Also adj., attrib. Editorial Note: Plural parerga. (source: Double-Tongued Dictionary)
Further reading
Secret signals on the job: Waitresses at some 19th-century restaurants ensured speedy drink service by communicating with a non-verbal code. One server took orders, then placed each customer’s cup to indicate exactly what the customer wanted...
The game of baseball has alway inspired colorful commentary. Sometimes that means using familiar words in unfamiliar ways. The word stuff, for example, can refer to a pitcher’s repertoire, to the spin on a ball, or what happens to the ball...