1. Roughly spherical or ellipsoidal body, produced as a result of local early cementation within a sediment. It is often found with a fossil as a ‘nucleus’. The size ranges from approximately 1 mm to more than 1 m, and concretions are generally monomineralic.

2. In pedology, the localized concentration of material, e.g. calcium carbonate or iron oxide, in the form of a nodule; such nodules are of various sizes, shapes, and colours.