n. - foodservice slang:

A monkey dish is the small shallow dish in which a side dish such as cole slaw or applesauce is served. The main purpose is to separate a cold or watery side dish from the main course, or to provide extra holding space if the main plate is full.

The name is derived from the idea that it's just big enough for a monkey to dine from. They are typically four-and-one-eighth inches in diameter and hold 3.5 ounces. They are not quite big enough to eat ice cream from, but they serve as excellent saucers for ice cream bowls.