Motor oil is the lubricant that keeps your vehicle's engine running smoothly. Although the term "motor oil" is widely used, there are many other names for this essential fluid. One of the most common is "engine oil," a term that's often used interchangeably with motor oil. Other synonyms include "lubricating oil," "car oil," "vehicle oil," or simply "oil." Some people also refer to it as "crankcase oil" because it circulates through the engine's crankcase. Whatever you call it, motor oil is vital for maintaining a healthy engine and preventing wear and tear, so be sure to change it regularly according to your vehicle manufacturer's recommendations.