Engine room stew was a food preparation, a type of stew created on board Starfleet vessels. Much like Engine room hooch, the stew was most often created by a member or members of the engineering department. The engineers on various starships would often create their own special versions of engine room stew, and people generally considered it better not to ask just what was in the stew.
After evacuating son Christopher from Elysium after a massive fire had killed the child's mother and stepfather, Charlie Pike brought his son some engine room stew to eat. After watching his son consume at least two plates of the stew, Charlie felt Chris would heal from the traumas he had endured. (TOS novel: Burning Dreams)