While the terms petroleum and oil are frequently used interchangeably in casual conversation, distinct technical differences separate their broad definitions. Petroleum—derived from Latin words meaning rock oil—specifically refers to the complex naturally occurring liquid hydrocarbon mixture found trapped in underground geological formations before any processing. In contrast, the word oil is a vastly broader category that can encompass crude petroleum, refined petroleum products, synthetic oils, as well as entirely unrelated organic substances such as vegetable oils, essential oils, and animal fats derived from non-fossil sources.