How are oil shale and shale oil different?

The terms oil shale and shale oil are distinct, though their definitions have evolved over time and can cause confusion.1

• Oil shale is a sedimentary rock containing solid organic material, primarily kerogen. It does not contain liquid oil naturally; instead, it must be heated to high temperatures (above 300 °C) in the absence of oxygen through a process called pyrolysis to release petroleum products.123
• Shale oil refers to the liquid product obtained from oil shale after it has been processed. However, since the early 2000s, the term has also been applied to "tight oil"—naturally occurring crude oil trapped within fine-grained, impermeable rock formations (such as shale) that is extracted using hydraulic fracturing.13

In summary, oil shale is the solid source rock, while shale oil is the liquid hydrocarbon product derived from either the thermal processing of that rock or the extraction of oil from tight shale formations.13