1. The elevation of the water surface of a river with reference to a fixed datum level. Hence ‘rising’ and ‘falling’ stages.

2. The major subdivision of a series. A stage is the fourth order unit in chronostratigraphy, the equivalent of age in terms of geologic time units. It refers to the body of rock accumulated during one age unit. When used formally the initial letter of the term is often capitalized, e.g. Frasnian Stage.

3. In palaeoclimatology, a climatic, and partly geologic–climatic, term usually defined by a series of sediments or a sequence of fossil assemblages and named at a type locality. For example, the Hoxnian (a temperate stage) is named for organic interglacial deposits at Hoxne, Suffolk, England.

4. The degree of development of a land-form or landscape over time, and which traditionally has been described by the terms ‘youthful’, ‘mature’, and ‘old age’ (see davisian cycle). The recognition of such stages implies an orderly evolution and this is now seen as unlikely for many parts of the Earth’s land surface.

5. The part of a microscope on which the specimen to be examined is placed. Normally it is flat and may be fixed, as in biological or metallurgical microscopes, or rotating with a 360° calibrated scale as in geologic microscopes. Transmitted-light microscopes have a hole in the centre of the stage through which light passes up to the observer from below. Reflected-light microscopes have an incident light system, whereby light is directed on to the stage from above and is reflected from the specimen to the observer.