Fossils are the remains or traces of organisms preserved in rock. The word "fossil" comes from the Latin word "fossilis," meaning "to dig up." Fossils typically are the mineralized remains of hard body parts like the skeleton of vertebrates or exoskeleton of invertebrates.
Generally, aside from specific external circumstances, soft body parts are not preserved as they are not partially mineralized at burial like skeletal body parts. The one exception is in Lagerstätten fossils, where organisms are buried in completely oxygen-free environments, preventing bacteria from decomposing the soft tissue. In addition to body parts, trace fossils can form, preserving feces or animal tracks given the right geologic circumstances. Chemofossils preserve specific chemical signatures indicative of biological material.