As is often done when investigating a new topic, it is important to learn the language pertinent to the topic. First, the word organic, in a scientific sense, simply means any material which is composed mainly of the element carbon (chemical symbol C). This is different from many other uses of the same word to mean, for example, grown without manufactured chemicals. In the scientific sense, organic materials can easily be manufactured materials.
Soil organic matter is simply material that contains carbon and is found in the soil. Most soil organic matter is natural, in that it came from a living thing at one time, but there may even be exceptions to this. The term humus can also be used in a very broad way, but here it will be limited to mean an organic material found in soil which is a product of plant and animal remains which have been decomposed and then synthesized into something new. The synthesis aspect of the definition is important because it is part of the reason that humus is quite persistent in soil. The other terms mentioned in the objectives section will be defined in context in the pages that follow.