Rocks formed from dead plants and animals that have been compressed are called sedimentary rocks, specifically organic sedimentary rocks.

Here's a breakdown:

* Sedimentary rocks form from the accumulation and cementation of sediments, which are particles of rocks, minerals, or organic matter.

* Organic sedimentary rocks are formed specifically from the remains of once-living organisms.

Here are some common examples of organic sedimentary rocks:

* Coal: Formed from the accumulation and compression of plant matter, primarily in swampy environments.

* Oil shale: Contains organic matter, mainly algae, that has been buried and heated over time.

* Limestone: Often forms from the accumulation of shells and skeletons of marine organisms.

It's important to note that the process of forming these rocks involves not just compression but also chemical and physical changes over millions of years.