1) Period or step in a process, activity, or development: as one of the distinguishable periods of growth and development of a plant or animal (the larval stage of an insect).

2) A period or phase in the course of a disease (the rash stage of Lyme disease -- R. H. Boyle); also: the degree of involvement or severity of a disease (advanced stage II or III disease, more than 10 positive lymph nodes found after axillary dissection-- M. S. Anscher et al).

3) One of two or more operations performed at different times but constituting a single procedure (a two-stage thoracoplasty). d: Any of the four degrees indicating depth of general anesthesia.

4) The small platform of a microscope on which an object is placed for examination.