Etymologically, the word is derived from the French compot, a mixture or composition.

As a verb, there are a variety of definitions and descriptions of the process: The aerobic decomposition and reconstitution of organic wastes into humus by the action of micro- and macro-organisms, involving the bonding of nitrogen onto carbon molecules, fixing proteins and carbohydrates in forms readily available to plants.

The word compost is now used as a generic term to describe any growth medium. As the collective name used to refer to a diverse range of different products and processes, compost can be a confusing and misleading term. A stricter and more accurate use of the word would perhaps be to describe compost by its humus content. Humus compost is a distinct and superior product when compared to many other growing media, which should really be sold as such on its own merits.

Garden compost, potting compost and fine seed compost all have distinctive and seperate uses and are not interchangeable. The infinite diversity of composts can be classified variously: according to the inputs to the process or source of materials, such as garden, domestic, municipal, industrial or agricultural: or by the end-use for which the medium will be used, such as for seed, seedling, potting on, potting up, cuttings, acid [ericaceous] or alkaline, special mixes for indoor growing, high-fertility for heavy feeders and formulations for specific types of plants such as cacti. Garden composts containing different manures will result in a variety of different properties suitable for specific types of crop. Concentrated fertilisers [organic or chemical] can be added to create quick-acting or slow- release mixes. Different production methods also generate specific qualities in the end-product, such as stacking, windrow, pit or vermiculture [worms]. Less accurately, the word is even applied to related processes such as loam- making, the formation of leafmould and even the anaerobic putrefaction of liquid wastes in cesspits and settling tanks [slurry].

The promiscuous application of the word compost to so many different materials means that anyone engaged in selling a compost product must label it explicitly and comprehensively to avoid inappropriate use. It is necessary to explain what ingredients the material consists of, where the inputs were sourced from and how it can be expected to perform. Most importantly from the perspective of growing organic food, it is necessary to explain whether the product is suitable for food use or whether it is only fit for non-food use in ornamental gardening. Accurate trades description of products means that customers will be less likely to use them in inappropriate contexts and will therefore be more likely to be satisfied with their performance and trust the producer with further business.