The soil is defined differently by soil scientists, and its definition has changed over time. This paper reviews how the definition of the soil has changed since the early 1800s by selecting and listing 81 definitions given in a wide range of soil science books, handbooks, glossaries, and dictionaries. Initial definitions of the soil were based on developments in agricultural chemistry or geology. The soil was seen as a production factor (medium) for agriculture that needed to be understood before it could be improved, or the soil was defined as disintegrated rocks mixed with organic matter. Definitions were rudimentary reflecting the overall level of understanding. Soil variation was not well understood. Overarching soil definitions appeared in the late 1800s following some major shifts in the understanding and knowledge about soils. The definition of the soil was particularly relevant for soil survey and in soil classification because it affected how soils were viewed in the field and represented in a two dimensional way (soil maps). Both the World Reference Base (WRB) and Soil Taxonomy have defined the soil, but standard field books describing soils often lack a definition. Most of the definitions in dictionaries and glossaries are detailed stressing the organic and inorganic part of the soil as well the origin, complexity, and some of its functions. Current soil definitions have a more environmental outlook reflecting the broadening of the soil science discipline but definitions will change following scientific advances and discovery. Soils are defined differently by subdisciplines. Considerable research is conducted nowadays outside soil science departments and research centres, and for some researchers the soil may solely be a medium—just as it was in the mid-1800s. The effect of increased specialisation and expansion in soil science causes the detail of the investigation to prevail over the idea of soil as a complex dynamic system that is part of a much wider Earth system. This review ends with a proposal for a scientific definition of soil, and a definition for lay persons and the general public.